It says untamable but this is a glitch, its gamebreaking. You use 20 tranq arrows and the game bugs a bit then you need to remove 4 stone pickaxes from your inventory and it says “tamed”. That is not correct though so you need to craft 5 stone walls in your inventory, game breaks again and you get to the ending. It glitches out again and you return to your spawn point with the tamed rockwell with you.