Ambre gives you 42 points of additional attack at maximum on two dedicated rounds (if you pill all your pills at Ambre rounds) - and Ambre itself is 6/5 card.
Morphun gives you 3x your pilling rounuds power on whole game, weighted towards match end and Morphun itself is 8/5 card.
As flat attack aid Ambre gives more sheer win-this-round force, but half ot the time Ambre does absolutely nothing and cannot stand on its own feet. Thus Ambre is extremly predictable and presents obivious weakness (card itself).
Morphun depends on the other cards power to gain great effect, Morphun delivers variable amount of attack aid after round 1. Morphun is quite decent card as itself with great power of 8 and decent damage of 5, thus it is not a weak spot on its own.
The main point about Morphun is that it's effect is not dedicated to any specific round but weighted towards match end. So Morphun can tilt the game easier because any error on opponent pilling can set opponent to downward slide. Player using Morphun "grows stronger" each round, Ambre delivers raw force on pre-determined rounds.