If you are doing gamma or beta and already have good Rexes you can use them and a yuty just fine. But for alpha I def recommend megatheriams. The gamma of this boss is insanely easy. I beat the gamma with Rexes with ascended saddles 9 k health and 450 meelee very easily like if this helps.

Ps for alpha you might want to bring a daedon. Make sure your megs have veggie cakes!