This has been brought up so many times before, it's not a bug just your first actual challenge. This is the best general advice I've seen posted here:

-SirPetrikov

The rhino is a guaranteed win no matter what you do.

The Devildog Chameleon portion seems to work as follows:

1.) Select Dog,

2.) Round one: use skill 2 immediately

3.) Round two Use skill 1

4.) Round three use skill 2 (dog should faint, if your hp drops under 8k, or if dog is still alive... back out and try again)

5:) Select Chameleon

6.) Rinse repeat method for dog,

(It is possible to get through the first portion with only skill 2, however I note this method as it has consistently worked for me.)

-Notes-

Suggested Power for the actual fights is 34k, If your team is exceptional, you may get away with pow as low as 28k. Be sure to have a poison wind and ignite on bench or in team just for sanity as the actual fights seem to almost require their use across the multiple fights.