Teenage Mutant Ninja Turtles: Shredder's Revenge

This achievement requires you to defeat Super Shredder on Gnarly difficulty, which is the hardest difficulty.

This would be quite difficult to do from start to finish, and especially hard playing solo, since losing all your health means you lose a life. In co-op, you can revive each other, which is huge for reducing the amount of lives lost.

However, there is a way to make this far simpler, although it is entirely luck-based: you can search for online lobbies, find one on Gnarly difficulty, and then join them once they're already pretty far through the game. Go into Arcade Mode, choose any difficulty (doesn't matter what you choose since you'll be joining an online game), and then press  to pull up online lobbies. For some strange reason, it only displays five lobbies at a time, so you can continually press  to see more. The difficulty of the lobby is displayed on on the left under the person's tag. Look for a Gnarly one, and ideally join it much later into the game. Check the percentage complete, and just for reference, the game is at 95% complete when the fight against Super Shredder starts, and it won't change until he's beaten.

As a side note, I played this game around two years after it released and I had no problems finding online lobbies at any time of day (7am on a Sunday morning or 9pm on a weekday). Granted, this game is still on GamePass as of writing this guide, but it seems to still be a reliable method of doing this. Gnarly games weren't very common, but over the few days I played this game, I found at least one or two Gnarly lobbies every day (Sunday, Monday, and Tuesday), so just be patient.

If you prefer to do this "legit" from start to finish, here are a bunch of tips to help:
 

• Play in co-op. If you have no couch co-op partner, at least play in an online public lobby. Playing with another person reduces the difficulty by a massive amount, both because you can revive each other to conserve lives but also because enemies can focus on one of you while the other recovers
• On the topic of recovering, you should be abusing  to taunt whenever you have downtime between fights. Every time "GO!" pops up on screen to move forward, take a moment for everyone in the group to taunt to fill their special meter so you have a  attack ready
• During boss fights, same thing. Any time the boss is doing something where you can't hit him, or is otherwise unable to hit you, spend time to taunt and refill your special. This is far easier to do in co-op too
• Utilizing the taunts as above, you can then restrict your attacks, especially on bosses, to only special attacks. You can't be hit or interrupted during these attacks, making them perfect for doing tons of damage but also avoiding incoming damage. For example, when a boss is vulnerable, you can usually pull off a combo of regular  attacks, and then if you try to do another combo the boss will interrupt you with an attack. To combat this, do your normal combo first, and then when the boss tries to interrupt you, do your special attack to interrupt him and do even more damage. This should be your go-to attack strategy for bosses (taunt while the boss does his thing, do a regular combo when he stops and is vulnerable, and then as soon as he tries to strike back and interrupt you, do a special attack on him, then retreat and repeat). I found this was the best strategy to avoid damage on Gnarly
• Use and abuse  to roll around. Basically, never walk towards an enemy. Always roll towards them and either chain that right into an attack, or roll behind them any attack. You can roll nonstop and just stop to attack when it's safe
• Save your special for when 4+ enemies are coming at you at once, or for particularly problematic enemies, such as the black foot soldiers or the large robot enemies that try to crush or grab you
• On flying enemies (the little bots in auto-scrolling levels), the easiest way to take them out is to use + to shoot up into the air, and then attack again in mid air with . This is typically enough to quickly destroy the small flying enemies. Trying to just jump and attack them is rarely effective, so use the jumping attack to take them out much more easily
• Never let yourself get surrounded by enemies. It's the quickest way to die. Always roll to one side of them and get them grouped on the same side as you. If you ever are surrounded, that's a great opportunity to use a special attack to clear them out
• Stay in the center of the screen as much as possible. The "obstacles" the game throws at you, such as cars, stampeding animals, etc., are at least telegraphed on the side of the screen, but sometimes enemies such as the spear-wielding foot soldiers will just come running in from the side with no warning and get a cheap hit on you. These can be really annoying, so stay in the center as much as you can to avoid cheap shots