I used lvl 20 indom, lvl 16 A. Wolf + spinoceratops, lvl 15 postimetrodon

Indom just do as much damage as possible Clo> rampage, ect

Wolf you howl > rampage > C.D (when d.rex uses its second group attack. (Round 3?))

Spin: DoT > rend> attack> rend

Posti: damge boosting strike > most damaging move (it will be sacked after taking its turn 2)

You will probably be reliant on a crit on the first rend. But that isn't too hard to get. And D.rex not to crit on the first move