I liked that in 2 they made attacking them to check pointless as if you attack a normal chest it would break and only give you trash, forcing players to actually observe a chest before opening/attacking it.
This guys great because he not only swallows you whole, he spits you back out naked, with all of your armor, items, and weapons unequipped. So now while he's still chasing after you and attacking you have to go scrambiling through the menu trying to reequip all your gear to finish him off.
I can't find an actual GIF of the attack, but lol.
Plant guy is from Metal Slug 3, the fish might be from eithe X or 3 as well. Metal Slug 3 also has a level where if you fajl down piranhas eat you and Metal slug X has a boss that is eaten by an Orca after you beat him.