Adrenalin and mitosis are like lifes backbone. They are the unique cards to the element unlike any other elements cards mechanics, with the exception of fractal. A simple frog or cockatrice doesn't do too much damage, and with no attacker in the 6-9 range, life relies of spamming attacks hard at the opponent and adrenalin does that best. You either have to choose between a couple dragons and cockatrices/frogs, lots of frogs and cockatrices, frogs/cockatrices and adrenalin, frogs/cockarices and mitosis for your damage outputs in life to get a 5-8 ttw average. Adrenalin is a huge card for life and I wouldn't say its rarely used.