The chameleon has the buff "Invisible", so it only receives damage from Standard Attacks and not Mysteries.

The strategy you should use here is to spam your Mysteries on the Hell Dog and kill it before it deals too much damage to your Gamabunta.

I came here looking for a way to beat it.

Using almost always W I was able to beat the summons easily and the rest of the Instance.

Team: Pain - Shurado, Pain - Tendo, Mei Terumi, Crimson Fist Earth Main

Just as I posted before in other topics about this instance.
in Gamabunta part:
- use W on Hell dogs when clone is present.
- do NOT use Q
- once you kill original dog, focus on chameleon
- use W on cooldown

For main enemies to pass (without blue circle)... this is what I used on my sorry alt... (btw, its shark bomb team...)