Bug Fables: The Everlasting Sapling

I recommend you don't try this fight on hard the first time around, as it can be very difficult.

Instead, wait until you are level 17 to unlock the skill move:

This move is really strong and can make the boss fights a lot easier. Be sure to stock up on good food before the battle begins. To refight any boss, go to the Bee Hive (In Defiant Root, take the lift just outside the northern town). Go to the room with the computer on the right, and select the boss to fight. The fight will be a simulation, but still, be the same. You also don't lose any food after the fight, so you can have the same inventory of food for multiple consecutive battles. To turn on hard mode, pause and go to medals, and equip the hard mode medal. Then just beat the boss, and the cheevo doesn't pop until you quit and return to the main menu.

Here's a link to this boss's profile on the Wiki: https://bugfables.fandom.com/wiki/Heavy_Drone_B-33