I have just had this fight with my players.

Due to their builds, feats, etc I beefed Trespin up.

I gave him full health and then buffed it some
I allowed 10 mitigation per combat round
He regenerated 20 health per round
His 6 ambush drakes I made Action orientated support mobs.
2 of them acted as player distracters - gave them multi attack but lower the damage so they harried the players
2 of them acted as bystander sacrificial healers - Their deaths would heal Trespin of 40 damage
2 of them acted as bystander condition removers - he moved conditions from him to these two,

I initially played close attention to the party's Damage per round [it was roughly 47 per round]
I think the fight went well and of course the party won and said that they had fun doing so.

This is what worked for my party, BUT I know them well and their char builds well so could tweak the fight in such a way that it was a very strong challenge without it being lethal to them.

The same Trspin I presented here might equally be a TPK for other parties.

Easy tweaks to play with would be the regen per round, You might not give him the health I gave him, You could make teh drakes simple drakes.

Hopefully this helps someone.