Save your biggest things like Mighty Guard for the final phase. As threatening as Discoid and Homing Missle sound, you can power through those forms without him even WSing once, or use healing trusts to recover that damage. Note also that with enough fast cast, it's possible to resummon trusts between forms.
Final form is the most dangerous due to how surprisingly good his magic accuracy is (lamps too). Unresisted nukes and debuffs (Paralyze, Stun, stat down) from 9 Dvergrs can bring you down pretty fast. He is, however, pretty weak defensively, and it's definitely possible to kill him from 75% with a good SC or something. I don't know how effective BLU debuffs like Terror, Stun, etc, but I wouldn't rely on them.
Regardless of what you do, I highly recommend bringing at least 1 person along in case you wipe. Like ADL, sometimes he just gets lucky with landing dumb crap.