Since I didn't have much access to the Genesis library in its heyday, I missed out on a lot of games, like Zool. So now, when I do get a chance to play them, I make sure that I tip the scales to my favor any chance I get.

So, in Zool, I pause the game, and hold in the Start button. Then press Down, Up, Left, Left, A, Right, Down (which kind of spells out the word 'Dullard'). The screen will light up halfway through the code, like it's been un-paused, but it won't be. Finish out the code an you get a bonus life! And, you can do this as many times as you want to stock up!

Easy!
Okay, The Little Mermaid isn't that hard of a game, but that doesn't mean that I'm above taking every advantage that I can.
Like going to the title screen.

Grabbing Controller 2, holding Right + A + B, and while holding those hitting Start on Controller 1. Done right, a new option should appear

Turning this game into a test of endurance.
A basic tenet of games based on movies is: most of them are awful. But sometimes you just have to play them to see how bad they really are. Like Jurassic Park.
But let's say that you get a game like this on a rental and don't have the chops to make it to the end before it has to go back to the rental place. What do you do?
Well, you could to to the title screen

And then grab Controller 1 and press Down, Right, Left, Down, Right, Left, Down, Right, Left, Down, Right, Left. Done right you'll hear a noise of some kind. Start your game like normal, and then any time you want to. Pause the game and hit Select. You'll be warped to the next stage!

And you can keep on doing that until you get to the end of the game (spoiler alert between these lines!)

Making the game last about three minutes (or less if you have fast fingers).
Money can be kind of hard to come across in the second Wizards and Warriors game, you don't really need it for much, but it's nice to have when you do want to buy something.
So, to make it easier to raise some cash, you could go to the title screen

Press and hold Up on the Cross Pad + B + Select, and while holding all of those, press Start. Done right, you can go to your nearest merchant and start playing the gambling game. The skull will always land in cups in the following order: 1, 4, 3, 2. And then repeat. You can sit there racking up cash for as long as you like

I was able to accumulate a tidy sum until I screwed up the rhythm and picked a cup out of sequence. Once that happened, the pattern ended and I had to go do something else.
Krusty's Super Fun House, like pretty much all the Simpsons games, is pretty tough. You have to take Krusty on a tour of the rooms in his Fun House to rid it of an infestation of purple mice. It's a puzzler, of sorts.
But say you get tired of the puzzles, or you just give up. You could start the game over and change the default password of "HI KIDS"

to the much less obvious " JOSHUA " (with a space at either end)

Which will let you enter any door in the Fun House you want. So just enter and immediately leave all of the different areas to instantly clear them. Then, head to the exit and marvel at how such a tough game could have such a lame ending.

I warned you!
The original Sonic the Hedgehog game, like pretty much all the games in the series, starts out pretty easy and then ramps up the difficulty to a ridiculous level pretty quickly. So it might be nice if you could practice those advanced stages, right?
Well, then good news!
If you go to the title screen

And press Up, Down, Left, Right on Controller 1, you'll hear a sound like you've collected a Ring. Then hold down the A button and press Start. Done right, you'll be presented with a Stage Select screen!

Letting you start pretty much anywhere you want.
Just be aware that if you start at the last stage and finish it, you won't see the true ending. You need to play through enough of the game to collect the Chaos Emeralds for that.
Dracula's a pretty tough customer in Castlevania, and if you die while fighting him, you only get very few powerups to fight him again, making things tougher.

But!
You could go back down the staircase leading to his chamber, and then back up again. If you do, the candelabras will reset and you can collect the powerups again. And as long as you don't walk far enough to the left to trigger the boss fight, you can repeat as many times as you want. And using some techniques I discussed earlier, you can really load Simon to the teeth with weaponry

Making this a slightly slower version of the method in Castlevania IV
Ever been playing Zanac and got just so far before you got frustrated and quit? Or maybe your playtime was cut short by a power failure or something and you had to stop before reaching the end. What do you do?
Well, you could start over again from the beginning, or you could power on the game, and wait for the title screen to appear

And then press the Reset button on your NES 13 times(!).
Done right, when you hit "Start" to bring up the Start / Continue screen, you can use the Left and Right arrows on the Cross Pad to choose whatever level you want.

Just be aware that you have to hit "Continue" to start on any level other than 1. Also, I couldn't start on anything higher than Area 10. When I tried to pick anything higher it'd kick me back to 10, so there's still a little bit of work to do, it seems.
If you've played through Neverwinter Nights enough to have gotten bored with the combat, you might consider spicing it up a little bit.
First, make sure that DebugMode is activated by hitting the "~" key and typing "DebugMode 1"

Then type "dm_cowsfromhell"

And you will summon... Cows from Hell to attack your enemies!

They don't do a lot of damage, but it is kind of neat to watch them spawn on the battlefield and then viciously attack your foes.
Occasionally when I observe people playing games with a joystick (especially in an arcade), I'll see them grab the joystick full-on with their hand and hang onto it like it's the only thing keeping them from falling off a cliff.

Which works, yeah, but it definitely hinders your experience by requiring that you use your entire arm to play which results in:
The solution?
Grip the joystick lightly between the thumb and the index finger, using the middle finger as well if that's more comfortable for you

You get more accurate control and don't use so much energy, which leads to longer playing sessions. It's totally win-win!