DeadWolf273, your answer is wrong. Pages list that keys cannot be dropped from Statue Monsters. Also, statue monsters don't drop their regular drops, they mostly only drop banners now except for a select few.
This is what I do for it: https://i.imgur.com/GV8DvKA.jpg It farms treasure maps and Crimson/Corruption keys. You can add/replace whatever biome you want. The jungle mud blocks at the sides increases spawn rate of monsters (Arapaima).
You need to be in water so the puddle is necessary, then my summoned minions can kill any monsters that spawn while I AFK. You could open it up around the puddle so you can kill the fish yourself but it might be dangerous if you AFK since they can jump at you, you could add honey in a bubble above the puddle though, or heart statues etc.. You can alter it however you want, the only important parts are having enough blocks for what biomes you want and the jungle biome for spawn increase, then the puddle to stand in.
I recommend if on hard to get traps from lizard temple and set the spike ball around you on a one sec timer and you in an closed box with 50 meteor around on both sides in the Crimson or any other bioms for other key molds.
Y=You X=spike ball trap Z=Meteor blocks 50 each Box 1/2=Any block Meteor heads will spawn around you and die from the traps and will drop stuff if needed you can add dart traps on both sides of you need