Is there any gem that reduces the health cost? Like would the one that reduces energy cost reduce it?
No but the health cost is minimal. Maybe it might for lower levels but I don’t even notice it
No, but if you use the off-hand Roar of Persuasion, that gives Life Drain whilst Wrath of the Berserker is active. The health gained from the Life Drain completely off-sets the health cost of Whirlwind that Fallow Field causes. As you can mostly likely maintain close to (or actually) 100% up-time on Wrath of the Berserker, effectively the off-hand negates the health cost of the main hand, so you can Whirlwind indefinitely.