Why is irenicus(tree of life fight) immune to spellstrike, etc?

[Question2]

When fighting irenicus at the tree of life i realised that he was completely invulnerable to any spells that lowered his spell or combat protections. This includes spell strike, breach, ruby ray of reversal, etc.

I used up 3 ruby rays and 2 spell strikes on him without his protections being lowered.

I had to kill him by mass spamming abi-dalzims which bypasses everything except MR(to my knowledge).

[Question2]

bump

[Creepin]

I'm not quite sure what exactly are you asking about: he is immune to this and that because game developers decided so, presumably to make him harder to kill, given that he's final boss

[Tempest]

Try dispel magic, then follow up with the breach. Not sure what his spell is, but that combo seems to work.

[Ammar]

Try dispel magic, then follow up with the breach. Not sure what his spell is, but that combo seems to work.

I think Spell Immunity Abjuration is only vulnerable against dispel. Not sure though.