Fill your inventory full of 20 stacks of mejo berries. Drop the peg in a box. Let it steal it all from you. Make sure it's 20 berries each at least or the taming will go down. Took me a good while to tame it. Take off ur armor and make sure to have health potions, whatever is in the far right box on ur hot bar will be priority to the peg. That's what it will steal. If you don't have anything it turns aggressive.

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