Battletoads

Six lives:
Hold Down + B + A and press Start at the title screen or continue screen. An explosion will confirm correct code entry. Alternatively, hold Down and press A, B, Start at the title screen or continue screen.

Continue game play:
Allow the continue timer to expire after one of the players loses all lives. Press Start on the next map screen to continue game play.

Control dragon:
Defeat the tool worker and take the stick/sword from him. Use that sword to defeat the dragon during the second half of level 1. Position your character on the dragon and press A to ride it. Tap A to fly and press B to shoot fireballs.

Immune to electric shocks:
Press B when next to your partner to pick him up and intentionally place him in any electric field. Your character will be shocked in the process. It is important that you are holding your partner while shocked. Reverse the process and have your partner carry your character into the electric field. Both characters will now be immune to future electric shocks.

Level warps:

Level 1
Quickly head butt the first pair of pigs, then run to the right to find a warp on the first ledge.

Level 3
Aim for the tenth wall on the fifth speeder course to find a warp to level 5.

Level 4
Fall halfway onto the first platform in the last section of this level. Then, quickly and repeatedly jump up to find a warp to level 6.

Level 6
Ride the snake as high as possible in the second section of this level. Then, run right, jump, and run right again to find a warp.

Hint: Destroying the Roto Blaster:
You can destroy the Roto Blaster in one hi on the second stage. Go up against the side until you turn into a ball and press Attack.
Information in this section was contributed by rwlter.

Hint: Double attack:
When either one of both players are fighting the two dragons close to the end of level 1, usually the two sticks acquired from those two walkers earlier in the level are left behind in that area while either player flies off on the dragons instead. If either one of the players has one of those two sticks in their hands when they board one of those two dragons, then they will actually take the sticks with them while they fly off on those dragons and they will use those sticks to attack. Instead of just the rather fast fire-shooting of the dragons themselves, you can also have the stick to attack with, making for an actual double-attack. Also, if you get close enough to the rest of the enemies for the rest of the level, you will then be able to dual-attack them that way.
Information in this section was contributed by Daniel.

Glitch: Zombie Battletoads:
Whenever either one of both players finish off the big walker at the end of level 1, have them fall down into the opening of the impact crater while the big walker is about halfway through exploding. Notice that either of the players will seem to have perished; yet, this is not case. They will then be shown still alive and ready to jump down into the impact crater for the next level. However, they will have seemingly empty energy as they do so.
Information in this section was contributed by Daniel.