This prestige only affects active abilities, except (somewhat disappointingly) observer siege mode
Zealot:
Move speed bonus while charging doubled (who cares)
Whirlwind deals 20 damage over 3 seconds (Pretty good against ground comps)
Dragoon is unaffected. Just costs more. Rip early game anti air.
High templar/archon
Feedback deals 2 damage per point of energy (so eats 2/3 of battlecruiser hp)
Psi storm deals 160 damage, and heals 100 shields
Archon merge takes 6 seconds (half as long. Pretty nice if you use HTs like calldowns)
Immortal:
Barrier absorbs 200 damage, 400 with the upgrade (I mean… cool? Not like anything ever punched through barrier anyway)
Reaver:
Scarabs build faster than reavers can fire them. (Scarab capacity becomes entirely useless.)
Phoenix:
Graviton beam cooldown halved (combined with 25 points in cooldown reduction mastery, graviton had 4 seconds of cooldown, allowing 1 Phoenix to chain stun 4 units indefinitely)
Tempest:
Disintegration deals 1000 damage over 20 seconds (didn’t get much use out of this one, but it seems not bad?)