Bettas- Will eat gills and toes off of Axies.

Cory Catfish(and other spiny fish)- If eaten, will lodge in the throat and tear/rip the inside, causing death.

Gourami- Will eat entire limbs off caudates.

Plecos- Will be eaten.

Fiddler crabs- Will either be eaten(possibly causing impaction) or will stress the Axie out when in the water.

Frogs- Will be eaten(can carry parasites, fungus, bacteria).

Ghost shrimp- One bite. Need I say more? They are a rather expensive snack which could cause compaction due to chitin in the shells.

Apple snails- Can trap Axie heads in their "door" and cut the axie's throat. May also carry bacteria and parasites.

Other newt larvae- Even if they are the same size, the Axie can swallow it's counterparts whole. Don't temp fate on this one.

Feeder fish- Can injure your Axie before being eaten. They have a propensity to nibble gills. If you choose to keep fish with your axies, choose non-aggressive fish like guppies or related live bearers.

Chinese algae eaters- Will suck patches of skin off of Axies! And probably be eaten too.