This card would be very fun to play with.
If it makes it into the game I think Life will have kind of a swamp theme with Giant Frogs and Giant Alligators running around. In any case both the card and the ability fit thematically. I think you have balanced it very well and done a nice job clearing up any confusion over ambush and adrenaline.
Alligators wouldn't replace Frogs or Cockatrice because of the 4
and the slowness to utilize the effect - which is a good thing - but they could be quite useful even without ambush in effect. They are adrenaline worthy, even when upgraded and so they could be quite useful. The obvious deck would be Forest Spirits and Alligators for the Life/Water synergy but it would be a slow starter.
Ambush aside, submerge would give life some more durable creatures. If you could pop an adrenaline on an alligator and then submerge it, that would be very powerful for an element with relatively weak creatures (Frogs, Spirits, Rustlers and scorpions....).
As stated before This would probably encourage Trios but there is nothing wrong with that. I can see an Alligator/Land Wyrm/Trident deck among others working nicely.
Keep up the good work OldTrees and crew.