In my Duel game on turn 28, I attacked an enemy hero stack in the open:
His stack: 4 Hv Cavalry, 1 Devil, 1 Hero
My Stack: 4 Hv Cavalry, 2 Giants, 1 Devil, 1 Archon
I lost this battle when I expected to win it. At first I thought it was bad dice. But on the replay, I saw all his units were +2 strength (7 strength Cavalry, 9 strength Devil) instead of 5 and 7 as mine were. The only explanation I can come up with is that his Devil negated my Archons hero Negation power.
That's not right as the Devil isn't meant to negate that skill or the Catapult/Battering Ram wall negation.
KGB