A constant spell affects the monster without the monster needing to cast it, and its duration is unlimited. If a constant spell gets counteracted, the monster can reactivate it by spending the normal spellcasting actions the spell requires.
AC 31; Fort +21, Ref +22, Will +21
HP 230
Duck Away(concentrate, move)
Trigger Stirvyn is targeted with an attack and is adjacent to an ally
Effect Stirvyn and the ally swap places, and the ally becomes the target of the attack.
Speed 25 feet
Melee Staff +24 (magical, two hand d8), Damage 1d4+6 bludgeoning
When Stirvyn casts a bloodline spell, a surge of ancestral memories grants either him or a target of the spell a +1 status bonus to skill checks for 1 round.
Effect: Bloodline Magic (Stirvyn Banyan)
Dangerous Sorcery
When Stirvyn Casts a Spell from a spell slot, if the spell deals damage and doesn't have a duration, he gains a status bonus to that spell's damage equal to the spell's rank.
Steady Spellcasting
If a would disrupt Stirvyn's spellcasting action, he attempts a DC 15 flat check check. On a success, the action isn't disrupted.