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Right, now I know that I've only really been talking in the context of FPS styled games and that's mainly because that's generally my favorite gaming genre but they aren't the only titles that include the ability to cheat or find hidden extras.
Take Pokemon Sapphire, it's a brilliantly perfect example of a game that still have plenty to offer the gamer way after you complete it.
You have the chance to catch 3 extra powerful legendary Pokemon but the process is incredibly long winded, effectively creating a second story line/quest objective. The only way of finding out what to do (if you don't already have a friend that's done it) is to actually read the instruction manual, something I can guarantee 0% of the children playing these games never done. Inside the instructions it had the alphabet in Braille (A series of bumps blind people use to read, for those who didn't know what Braille was) and it was up to you to decipher the codes that the game developers had left for you. Most of which involved you using different HM's in specific places to unlock certain doors however the first and most difficult code was the simplest: 'First comes Relicanth, last comes Wailord', it seemed pretty self explanatory, put these two pokemon in your party, first and last, the Wailord part made sense but as I was a child who didn't get the internet til I was about 13 I didn't have a clue what a Relicanth was, neither did any of my friends, to my struggle I found out it was an incredibly rare stone fish that had under a 10% sighting chance and then a 3.3% catch rate, without a doubt it had to of added at least an extra 50+ hours worth of play time, none of which I regret as I was the first of all my friends in and out of school to get all the Regi's.
The Regi's of course wern't the only extras to Sapphire, it had the Sky pillar which involved multiple bike oriented puzzles and even the folklore behind Latios and Latias (depending if you had Ruby or Sapphire), it was the first game I owned to make me want to 100% everything, I loved the idea of having all this extra stuff built into the game, looking further into this led me to discover what Easter Egg's were and that quite a lot of games had them.
Now as far as Easter eggs go, Halo has by far the... eggiest? This weird floating ball covered in letters and numbers can only been seen if you get outside of the map and fly up to the far right laser pillar, it's known as the Da Vinci code egg for whatever reason, I'm pretty sure the letters and numbers are all just random.
In all Halo games if you flip over your vehicle it gives you the option: Hold RB to flip. But on the level Sandtrap in Halo 3 there are these 2 massive tanks called Elephants that carry smaller vehicles on them, you can drive it around but only at an incredibly slow pace, in forge however if you spawn enough explosives on one side and blow them all up you have a small chance to flip the elephant and see this quirky little message. Game developers also had a running easter egg that would change every so often on the Valhalla map:
- January 1st: Make Love Not War
- April 22nd: A skull with a recycling sign.
- May 5th: Toady Was Live!
- July 4th: BBQ at Bob's Place
- July 7th: Seventh Column Symbol.
- October 31st: A grave stone reading R.I.P."
- November 11th: Kilroy Was Here.
- December 25th: A Christmas light with an X on it.
Halo didn't just have Easter eggs though, like Pokemon ruby and sapphire it had some built in extras know as skulls, after finding them in their various locations on each map you could apply them before starting a mission, each skull would apply a different ability for the campaign, usually to make it more difficult in some way but also add a score multiplier, enemy's have double health or you can only regenerate your shield by punching bad guys for example but their were 4 silver skulls that made the game slightly more interesting my favorite one was of course 'Grunt Birthday Party' because every time you get a head-shot on a grunt a bunch of confetti would puff out and you'd hear a bunch of little kids cheering. It was one of the most rewarding feelings to consecutively pop a bunch in the head and hear: Yaay!! Yaay! Yaay!! Yaay!! Yaay! Yaay!!
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To conclude, gaming has come a long way in a short amount of time and unfortunately it's quite a niche thing to be into glitches so game developers try much harder to remove them, it's not a bad thing if it makes the game smoother to play but when it's something harmless that can give major advantages to the people that know about it, I say leave 'um be.
Referencing:
http://www.psypokes.com/emerald/legendaries.php
http://bulbapedia.bulbagarden.net/wiki/Relicanth_(Pok%C3%A9mon)
http://haloeastereggs.net/easter-eggs/halo-3