Hmm. OD and adrenaline works really weirdly actually. The attack increases with each attack, but each increased attack gives the creature less attacks. I saw 5, 6, -3 damage from a pest with 2 attack (from eclipse) when I hit end turn. It ended with 11 attack. Yeah. Negative three.
I guess on the first attack, it increases to 5 and does the 5 damage. On the second, it increases to 8. A normal creature with 8 attack and adrenaline will do 6 damage on the second attack, so that makes sense too. However, a creature with 11 attack only does two attacks. That's probably why the third attack did -3.