What I think would be best not just for the overseer but the tek cave in general, bring 10 rexes, 10 megatheriums, 9 therizinos, 10 spinos, 1 otter completely leveled up in melee, 2 yutys both on auto courage, 4 mammoths (make sure all herbivores have at least 5-10 veggie cakes in their inventory), 3 daeodons, 1 dodo. Level them all up to 50k health, 7k melee. First lead all the rexes alone to the terminal and leave the rest of the army next to the closed door on the inside, the rexes will clear the path. Then go back to the door, leaving behind the Rexes at the terminal, lead the yutys, mammoths, and daeodons to the terminal while holding the dodo. Then go back and lead the megatheriums to the terminal. Then do the same with the therizinos. Repeat one last time with the spinos. Got everyone at the terminal? Good. Now time to fight the overseer. Be sure to do all this with your otter equipped for insulation. Lead all your animals to the fight and enable passive healing on the daeodons, then send everyone to fight the overseer. The Rexes will finish the megapithecus, the megatheriums and spinos will finish the Broodmother, (make sure you yutys are on passive, they are there for their courage roar) the therizinos and rhinos will finish the dragon, and the mammoths will use indimidation on enemies. If you followed everything correctly, you should defeat the overseer with zero casualties.

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