Our rexes had 80k HP and 6k% damage which is 2k per bite. We had lost 3 of rexes. Beta Dragon.
The Dragon isn't the only thing you should worry about. The dimorphos will kill you off your mount if you don't have a good armor. It is better to bring a lot of people to mount rexes, as about 2 out of 3 rexes died in lava. They just stand in lava and bite the Dragon. Reaper could be good if you have one(for killing dimorphos), but prepare to lose it - Dragon ignores its natural armor. Good luck, survivors.
Bring Therizinos instead of Rex’s, since herbivores take reduced damage from the fire, and can eat sweet vegetable cakes to regen health quickly. Take about 17-18 theriz, 2 hell pigs, and 1 yuty as well as an OP rocket launcher or shotgun, or substitute 4 theriz for allo’s to get the bleed attack.
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+.
16 Rex 2 pigs and yuty hard boss fight on rag is so easy when u get the 10 riders 1 guy on a pig with other following make sure it's full food and has food in inventory... Rex's must be 30k health and 600+ attack JM saddles or better is advised 1 yuty rider high standards to keep all boosted .. everyone else on Rex . Yeah b make sure pigs DO NOT Let anyone else whistle them pigs for healing not attacking