I suggest this :
If you cast 2 time's adrenaline on a creature it dies (Overdose, the heart explodes, like in real life
)
It would be very cool:
1. to counter adrenaline with adrenaline.
2. Life will have at least first creature control
3. Green Nymph will be more playable.
4. It's kinda new, but cool idea, improve the gameplay and good parallel between real effect of adrenaline
If you think it may be to powerfull, you can add the restriction that you can apply only 1 adrenaline per turn.
So you'll kill the enemy creature with the cost of extra-damage to that creature for 1 turn