Everyone here talking about Rex’s this and Rex’s that is foolish. Maybe 4 Rex’s to tank a little and the rest Mut Theriz packed full of Veggie Cakes. The fire melts the Rex’s even with ascended saddles. And all our Rex’s were 35k hp+.
Use as many therizinos as you want since it does extra damage to carnivores technically since the therizino is an omnivore which means carnivore and herbivore put together so since the other half is herbivore it should block out that affect I would also recommend pumping damage and health. Thanks for using your time on my tip I hope it helps you beat the boss.