you can either fight, and lower its hp enough to catch it like a pokemon (then you can make it a familiar) or run away if this is not what you're looking for.

pest's turn! pest used tackle! pest head butted Blue Moon! 45/50 hp remains your move!

Pablo attacks; feeding frenzy plagues leading charge *ability*

a giant wrym erupts out of the ground and roars ferociously! it will now do 20 damage to the pest every turn! 20/40 hp remains for pest!

pest uses tackle! 30/50 hp remains for Blue moon! your move!

using his water manipulation abilities, Capsule rains a shower of water droplets upon all enemies!

~PEST DEFEATED~ all your characters earn 50/100 exp, so they don't quite level up. what would you like to do now?

are you looking for a leviathan? or lionfish venom? i'll just assume you are.