Build bridge on the surface, pull planterra there, fight it on a bridge. That's how I killed it on mage, on melee I killed it standing in honey+campfire+heart statue+turtle armor+star cloak+charm of myths+ironskin/regen pots, that was first kill and no twinking, granted you might have to farm to get the items if you don't have them already(bunch of mimic drops mostly, and finding a heart statue might take a long time). Can definitely kill it with a bridge as "melee" though, craft the 5 light discs or whatever the name is, the 5boomerangs, and just spam them while you run along the bridge. Works the same way, Planterra is fairly easy to beat on a bridge, in phase2 she does bursts of speed to catch up with you but with lightning boots she generally ends the burst before she reaches you(or you can jump obviously). Bridge doesn't have to be too long, like 250blocks should be enough, need wings to turn though.
I've tried the teleporter shit but didn't like it, too often she hooks into the teleporter and you get fucked. Can beat it if you dig a large enough room underground kiting in a circle but it's unnecessarily harder than the bridge.
