Cave Fillet is the last stage in Sea of Tuna.
1 Those Guys will spawn every 40~80 seconds. After dealing around 10k damage, Teacher Bun Bun spawns as the boss with Dark Emperor Nyandam and a One Horn that continues to spawn every 40~60 seconds. Pigges will join in later and respawn at a slightly slower rate in comparison to the One Horns.
This level requires some luck, particularly if you don't have any True Forms/Crazed Units. Delinquent Cat and Bodhisattva Cat can be a great help, as they can help stall the movement of Teacher Bun Bun. More meatshields also help in this level when close to your base.
If you want to use sufficient long-range attackers, sending out constant waves of meatshields is crucial. If the waves of meatshields are not constant, Dark Emperor Nyandam may move up and kill all of your long-range attackers in one hit. If you have Megidora, it'll help you a lot, so be sure to level him up as much as possible.
Also do not bring any cats that knockback floating enemies! If you knock back Bun Bun, all of your units will move into the range of Nyandam and get killed.
It is recommended to buy Boogie Cat at this point, because without 2 or more meatshields, the upcoming stages are very difficult. If you do not wish to use cat food, try to get cats from event stages like Faster Than Fast Food, The Crazed Cat/Tank, any stage of All Hallow's Road, or do the Rare Gacha when limited edition is part of the pool.
Again, Sniper The Cat works well in this stage all together. It can kill the Those Guys at the beginning. This can allow you to stall for money quite effectively with out spawning a single cat. Once you reach max, you can start by spawning Meatshields and then ramp into more effective cats. This strategy can even be done without anti-floating cats, your cats should be powerful enough to defeat Teacher Bun Bun and Dark Emperor Nyandam. Can be used in conjunction with other strategies. Recommended for beginners.
Strategy for 3-Star Level
Use 1 Crazed Wall Cat to slow down Those Guys. Once the Crazed Wall dies, send another one. Keep this until you have maxed worker cat and maxed money. It's not recommended to stack up Bahamut Cat at the time, because the rate Those Guys come out is too slow. Then summon all the cats you've brought. It is recommended to have Paris Cat, Dancing Flasher Cat, Crazed Macho Cat, Crazed Wall Cat, Crazed Bahamut Cat and any Uber rare you have. (PS: I have used The Majestic Zeus and Super Galaxy Cosmo.)
Sniper the Cat, while not always needed, works well here if you don't have any Cat Combos that can boost research. Also, do not attempt this level if you don't have Sanzo as his slow is required to stall the Bun Bun. Use at least 1 'Strong Up' Cat Combo, and if you have it, 'Research Up' (I personally didn't have it). The main focus on this strategy is to slow Bun Bun with Sanzo Cat, while chipping him down with Cameraman Cat and Awakened Bahamut Cat. However, do remember that Nyandam is still the major threat in this level, as knocking back a slowed Bun Bun will cause Nyandam to destroy your front lines. Pirate Cat's true form is also recommended here, as it can push back the One Horn, Pigge and stop Nyandam's attack in intervals. If you don't bring the research combos, bring 2 meat shields and Maximum the Fighter (Viking Cat's true form) or any other rare cat which is strong against Red. How to Play: Stall Those Guys until you have max wallet, then prepare to beat one of the tougher 4-star stages around. ALWAYS spam Sanzo and Cameraman until Bun Bun dies, while spamming Pirate Cat and your meatshields (5th cat if you're using research up). When Bun Bun is slowed and Nyandam has just attacked, release Bahamut to chip away at Bun Bun. Rinse and repeat this until it eventually dies. The battle becomes 100% easier after this, just spam Cameraman Cat and all other cats until Nyandam is behind the enemy base or dead. Congrats, you just beat Sea of Tuna 4 stars! Have a sandwich and go outside.
4-star Strategy 2
Line-up: Cool Japan (cats can be any level.; they won't be used), Awakened Bahamut Cat (or any cat really just need something to fill in that last box in the first row), Cataur, Cameraman Cat, Maximum the Fighter, Ramen Cat, Jiangshi Cat (these five cats are lvl 30)
No power-ups needed
Do not spawn anything at the start. Let Those Guys hit your base while you upgrade your Wallet. You can use your cannon as well as you won't need it in the main fight. Once your Wallet is level 8 and full, spawn a Cameraman to kill Those Guys. Then literally just spam all five cats in the second row non-stop. Prioritize Jiangshi, Cameraman, and Maximum though.
Upon base hit, the boss will appear along the red enemies. Prioritize Maximum and Jiangshi until those red enemies die. You can stop spawning Maximum once they die and just spawn them after red enemies reappear. Although Maximum can still tank and deal some minor damage to Bun Bun, so you can keep spawning him if you want.
Just keep spamming and you'll win.
Note: Cataur is just there for extra help. He isn't really needed.