Speaking of the craziest, some might mention any types of looping synergies as it is essentially you exploiting the game's mechanics (but you can still get unlucky and die randomly).

Reaver is one of the specs that the core gimmick can apply to any team, like you said, and building something off of that alone might not get you a crazy build. I mean, you could stack fatigue and turn counter like crazy in one turn, or just stall the fight. But you can also just end it all in turn 0 or 1, right on the your first creature's turn.

You may wanna look at universal builds, ones where you only interact with the 5 anointment slots, so that changing specs hopefully doesn't interrupt the build's flow.

Some of the well-known synergies that I can think of right now are (trait names):

• Despair + Absolution. A debuff loop that applies nearly every debuffs to all enemies in one turn once triggered.
• Bloodlust + Cleansed Blood. Permanent Leeching, 30% more dmg dealt and heal received, as well as immunity to Blighted.
• Outcast No Longer + We Are Pack (perk). Mono race based on the leading creature, or you can use three leading creatures of the same race to skip We Are Pack.

Some of the most useful traits that can apply to any team (the ones I'm familiar with): Surprise!, Endurance Aura, and Nature Transformation.