For as long as there have been video games there have been systems in place to ensure that those video games do not continue on unabated. After all, what good is a truly endless experience, an interaction without incentive? Once the initial novelty wears off, what then? Without the likes of the humble health bar to affirm our actions, to measure our gaming greatness, we'd all be utterly bored by now.

Health bars - hidden or otherwise, are as vital to gaming as the lifeblood in Zelda's HUD hearts are to Link. They come in many forms, measuring our proximity to defeat in everything from blood to - well, everything listed here. Yes, you see as games have evolved, so have our means of measuring our ability - or not - to play them well. New stories, worlds, tasks and design ideas have forced the noble health bar out of its comfort zone and demanded that it adapt, to measure all kinds of different successes and failures in a plethora of new contexts. All pretty much hit you with restart hammer when depleted, but it's not the destination that matters, it's the journey. Thusly, today's big list of things looks at just some of the many, highly intriguing alternatives to the classic life bar. Whatever you do, don't let 'em hit zero.

They say that 'the heart wants what the heart wants', and what the heart wants most of all is not to implode out of sheer bloody terror. An EKG, or electrocardiogram device, measures the rate at which that most vital of vital organs operates. It's also rather useful for telling medical professionals when to start beating on your chest like an angry ape. Fear Effect uses the machine's iconic pulsing symbol in lieu of a regular health bar, with enemy attacks serving only to increase its rapidity. Green is good, blipping along at a steady rate, whilst red and yellow represent a state of declining health.

Players can enhance their chances of survival by 'calming down' the protagonist - either by way of stealthy play or through the completion of in-game puzzles. Failure to do so will effectively cause your avatar to suffer a massive and fatal heart attack. We're not exactly sure where science stands on the whole 'death by fright' debate, but it's a fair bet that the game's lithe leading lady hasn't been wolfing down any deep fried mars bars lately, so it can't be her cholesterol to blame…

If only every individual came complete with a sanity meter. It'd certainly make relationships a whole hell of a lot simpler. Knowing your ditzy misfits from your grade-A nutters is an evermore-essential skill. With access to the heady world of online dating, the average person's exposure to amorous lunatics has increased exponentially. This sort of thing should be a default widget on everyone's profile.

Video game sanity meters have been around for quite a while now, though few are held in such high regard as that which appears in Silicon Knight's Eternal Darkness. The concept proved to be so darn popular in fact that Ninty even opted to copyright it, presumably so that they could accurately gauge lost Metroid fans' continuing levels of despair. Unlike many of the entries on this list, ED's meter isn’t an outright replacement for the health gauge, though failure to top up your 'mental mana' will cause all sorts of freaky disturbances to appear, eventually leading to your death. Contributing factors include being spotted by an enemy, or witnessing a terrifying event. Thank God nobody asked the protagonists to play Too Human then…

If there's one fatal flaw in the whole 'average everyday hero' trope then it's this: real people tend to be absolutely bloody awful at handling pressure. Heroes undergo great pains to achieve their ends, overcoming fear itself in the name of goodness, truth and the philanthropic spirit. Real people smash up their keyboards and scream highly specific grievances at their pets. See the difference? A hero's courage isn't for everyone. Some folks have it, most don’t. Where the likes of Nathan Drake can happily laugh off a good dozen-or-so near-death experiences (seriously, did he piss off Death from the Final Destination franchise?) most of us would sooner be reduced to an amorphous wailing wreck.

So it's rather refreshing to find a game in which our avatars actually do the same. Capcom's Clock Tower 3 even includes a 'panic meter', which fills up any time that the lead character of Alyssa encounters one of the game's many monsters. Unlike the aforementioned sanity meter however, this mechanic can actually cause lil' Ally to become damn near-uncontrollable, as she sobs, stops, trips and outright refuses to listen to reason i.e. 'use your health potions' or 'hide over here'. Sounds about right to me.

Lawyers, as a rule, tend not to lack for self-confidence, though honesty is another matter entirely. (*He says, before being sued for 18 quintillion dollars*). It's interesting to note then, that the Ace Attorney franchise isn't so much concerned with the protagonist's self-assurance as it is with the confidence he can inspire in others - namely both judge and jury. Likewise, prosecutor par excellence Miles Edgeworth requires the absolute truth in order to claim victory. Talk about Opposite Land... Still, these concepts remain vital to the series' success, forcing players to really do their homework in order to succeed, as opposed to when playing more, shall we say, 'accusation-happy investigators'. Alright we're talking about you Cole Phelps. You'd never have worked it out on your own.

Also known as the 'penalty meter', these gauges reflect how far the player is from earning him or herself an instant failure. Rather than 'dying' outright, the presiding judge will instead order the player to simply shut up, thereby preventing any additional evidence from being exposed. Lack of facts means a lost case, no matter how well things were progressing up to that point. Penalties can be incurred in a number of ways, though most relate to proper lawyering faux-pas - i.e. presenting irrelevant information, causing numerous interruptions or generally wasting everyone's time.

How ironic that a game as maddeningly frustrating as Dr. Jekyll Mr. Hyde's NES 'adaptation' should include its very own 'anger meter'. Perhaps they ought to have stuck one on the front cover, next to a shot of that man's head exploding in Scanners. 'Anger level: Dome Blaster'. As it stands, the game's actual anger meter measures how many hits Dr. J - no, the other one - can endure before morphing into his alter ego. Once changed, Hyde can only revert to his human form by defeating scores of enemies, lessening his anger with every successful kill.

The aim here is to help either persona to reach the church. Jekyll is on his way to get married, while Hyde appears to be terested in battling floating demon heads. J sidles to the right, overcoming the usual assortment of church-goers' woes - namely attack dogs and laxative-gulping birds, while H shuffles his way to the left, fighting off all manner of hell spawn in the process. While the game does boast an additional health bar, most folks aren't really likely to notice, so busy will they be slamming their skulls into the TV in vexation.

A solitary 'health bar' shared between as many as four cack-handed friends? What could possibly go wrong? Rock Band's crowd meter is all about giving the people exactly what they want - good music, played in time, with a minimum of drug-induced tirades, prissy refusals to play or other such rockstar-related nonsense. Failure to keep the tunes coming results in your immediate death.

No wait… you're just made to start all over again, like the world's crappiest cover band freaking out at a high school talent show. Potential hits to the meter include everything from missing big notes to the police happening upon that one dead groupie at the back of your tour bus. No, not really. You'll have to wait for Rock Band 4 for that...

Ah the morality meter. What better way to adjudge ethical integrity than to plot the entirety of human experience along a single, simplistic gradient? "Have you been a good boy this month Mr. Manson? Well then I guess we can let those nine most recent murders slide. After all, you are a level 87 paragon". I hope that no one's actually taking their cues from these sorts of things, paying off the occasional genocide by helping a couple of ducks to cross the road.

So, what exactly is a morality meter doing on this list anyway? Surely those things are so far removed from the typical health bar as to warrant their own article? Well yes, for the most part. While it's true that ethical flubs seldom result in an outright failure, some games do choose to punish players long before the alternate endings roll in. Take the Adventures of Robin Hood for example, an MS-DOS game that for some strange reason allows players to turn a man a legendarily benevolent man - so altruistic he's practically an adjective for charity - into a right old greedy bastard. Accordingly, the townspeople could also play against type, by stringing up this bizarro Robin of Loxley by his neck. You didn't see that in the Kevin Costner film.

Despite being named as a 'Sanity Meter', Fahrenheit's unique take on the concept is really more akin to a 'stress gauge'. If the likes of Amnesia and Eternal Darkness can be considered 'straight horror', then this cult hit is more of a twisting and atmospheric thriller. Everything from guilt, to grief, to outright physical revulsion can cause the game's main players to lose stability, edging them ever closer to complete mental collapse. In short, where sanity meters are perfect for measuring shocks, scares and unbearable tension, a stress gauge instead assesses the slow decline of an everyday office worker. That is to say: everything up to and including their big, monitor throwing rage quit.

Interestingly, or should I say rather morbidly, the game doesn't shy away from displaying the results of these overloaded stress meters. Depending on the protagonist being played, as well as his or her current situation these outcomes can include suicide, arrest, job loss and even committal to a mental asylum. Ouch.

The first time I saw a tiny man pop up onscreen and yelp "Toasty!" during a brutal fight to the death, I instantly understood that the Mortal Kombat series likes to have fun with its secrets. What started out as a few easter eggs - a fleeting glimpse of Reptile here, Santa Claus flying in front of the moon there - has grown into a massive collection of clever throwbacks and cameos that'll skewer your brain's nostalgia receptors and splinter your funny bone (in a good way). And has over two decades of franchise history to reference, so you better believe it's got tons of amusing secrets and nods to the previous games.

In fact, some are so well-hidden that most players probably won't even notice them. I've rounded up the coolest (and most obscure) tidbits I could find in MKX, and you should know that many, many fighters died to bring you this information. Revealing these to your uninformed friends is sure to recall that old-school feeling when you knew the Fatality inputs and they didn't. Read up, then pass it on to your fellow kombatants.

If you've played through MKX's story mode, you might remember the scene where Sonya visits Jax as one of the least violent moments in the entire game. The grizzled Special Forces veteran clearly wants a simpler life, clad in farmer's overalls, tinkering away at an old tractor. But it seems like Jax also has a soft spot for two of the most advanced pieces of technology in the Lin Kuei ninja clan, judging by the 'Uncle Cyrax Stone Ground Mustard', 'Old Sektor's Ketchup', and 'LK-4D4 Engine Oil' posters hanging on the wall of the Briggs family's barn. Who knew these cyborgs were in the condiment and car repair businesses?

MK diehards will likely know that Tremor - a forthcoming DLC character with the power to cause earthquakes - is actually a throwback to Mortal Kombat: Special Forces, a spin-off brawler starring Jax that's among the . But what you might not know is that Tremor was actually playable once before, in a very unlikely venue: the handheld arena. By plowing through the Challenge Tower in the PlayStation Vita version of the ninth Mortal Kombat, you'll eventually reach Challenge #100, which (very briefly) puts you in control of the brown-clad, earth-bending ninja. And of course, he's going up against Jax.

This bit of character development is done in such a low-key way that 90% of players will probably miss it entirely. But kudos to Netherrealm Studios for debuting their first gay fighter in the Mortal Kombat franchise: Kung Jin, the smartaleck younger cousin to Kung Lao and an ace with his magical bow. During the story mode's that this dialogue is indeed a bit of very subtle exposition.

Whenever this pale-skinned Netherrealm sorcerer warps onto the scene, he's usually carrying a dagger and the severed head of an ogre-like creature. Those aren't props he bought from Party City in an attempt to psyche out his opponent - that poor decapitated monster is actually Modoch, the giant Oni sub-boss from Mortal Kombat: Deadly Alliance. It's never stated why Quan Chi felt the need to behead his minion 25 in-game years after the fact, though. Maybe Quan Chi decided that Moloch was too generic an MK character to keep on living.

Erron Black, the cowboy-looking bounty hunter loyal to Outworld's Kotal Kahn, typically relies on his trusty pistols during combat. But Erron can also switch to his Outlaw variation, where he brings a sword into battle to do a little stabbing in between all the shooting. This blade is actually formed from a Takartan's arm, the creatures (like Baraka) who can pop giant cleavers out of their forearms, Wolverine-style. Hopefully, Erron posthumously removed that Takartan's arm-blade, because otherwise... ouch. Also, the animation when Erron does his Takartan Stab command grab bears a striking resemblance to Sub-Zero's from the 2011 Mortal Kombat.

The MKX cast is chock full of talent, including some actors who you probably know from their many video game voiceovers. See if your ear picked up on all of these: Shinnok is voiced by Troy Baker (Joel from , pretty much anyone from any AAA game ever). Cassie Cage is played by Ashly Burch, who you probably know as Tiny Tina from Borderlands 2 or the titular sibling from Hey Ash Whatcha Playin'. Tricia Helfer, aka Number Six from Battlestar Galactica and EDI from Mass Effect 3, does an excellent Sonya Blade. And then there's Steve Blum, the Guinness World Record holder for most video game roles, doing his trademark gravelly voice for Sub-Zero (and a raspier tone for Reptile).

If you haven't seen the live-action Mortal Kombat flicks, you missed out on a particularly outstanding example of a cheesy video game movie one-liner. When Johnny Cage goes up against the hulking Goro, the four-armed brute snatches the shades off the Hollywood star's face and crushes them with a scoff. Johnny's retort during the ensuing fight scene is priceless: "Those were $500 sunglasses, asshole." Cut to 25 years later, and Cage is still bitter, saying "Don't you owe me some sunglasses?" before a match with Goro, or referencing .

Let's cap things off with a trio of easter eggs all related to Cassie Cage, daughter of Johnny Cage and Sonya Blade and the de facto leader of MKX's new generation of fighters. First up, you might've noticed that Cassie always removes some iPod-esque earbuds before a fight, which are presumably hooked up to an MP3 player tucked away in her gun holsters. And if you listen very, very closely, you can hear those earbuds blasting tunes from Mortal Kombat 3. Not a bad choice as far as prefight pump-up music goes.

Of all the Fatalities in MKX, Cassie's 'Selfie' finisher might be the most gruesomely hilarious. Long story short, she smashes her opponent's jaw till it's hanging by a hinge, then grabs their going-into-shock body and snaps a picture posing with her kill. The camera then zooms out to show that she's shared this mortifying image on her Facebook-parodying Friendships page, which has a rainbow logo in reference to . If you give it 30 seconds or so, you'll notice a stream of randomized comments popping up under the post, including (but not limited to) a Stryker cameo, a message from Noobde (the Twitter handle of MK co-creator Ed Boon), and Cassie's mother asking why she's friends with Kano on social media (y'know, the Cage family's most hated rival).

The Klassic tower is essentially MKX's arcade mode, and completing it rewards you with a brief slideshow ending for your chosen character. These are filled with cameos from old MK characters, like MK4's Taven in Kenshi and Takeda's epilogues. But the most interesting run-in happens in Cassie's ending, where Raiden tasks her with "hunting down a soul stealer." The intended target is implied to be Shang Tsung, but Cassie tracks down and offs an old man who, with his dying breath, identifies himself as Shujinko. If you played Mortal Kombat: Deception, you'll remember Shujinko as the protagonist in the expansive Konquest Mode single-player campaign, where he had the power to steal his opponent's moves (just not their physical form). An unfortunate case of mistaken identity, then.

And of course, there's Johnny Cage's alternate Ninja Mime costume, where he reprises his most well-known Hollywood role. Have you found any other excellent secrets or references in Mortal Kombat X? Share them in the comments, and we'll be sure to update this list with your suggestions!

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