Regarding tactics : this is the time for Waymar's gear list to shine!
- He has Nerveskitter 1/day to go first
- He can activate his Crystal of Temporal Acceleration, and use those two rounds to put two Explosive Launcher rounds in front of the undead + draw his Launcher. Then he can use his final action to shoot his final explosive round, detonating them all in the enemy's face. Then he can do the Quickened Maximised Fireball thing @Goldfish suggested, use his move action to move into melee, and use a swift action to activate Belt of Battle to get a Full Attack in (and he has Haste active already, which is nice). If needed he can use a Swift action from inside the Temporal Acceleration to activate the belt, because nothing actually says you have to use the Belt right them (you just have to use it before the end of your turn, but you can take actions in any order you want).
- He already has Blur active, so I didn't include another defensive buff. Thoughts? That Warding Shield spell could give him SR 26, IIRC.
EDIT:
@Goldfish, burning a bajillion spells for Arcane Strike feels a little cheesy. That "free action" is a relic from the old action system (if it had been published later it would have been a swift action, and you know it), so let's not game it too hard.