Eggs

In the first case, it is impossible to lose, because the computer does not inflict any damage.

Mana might run out. Even if you replenish it using Rage and Concentration, these sources are still limited after a certain round, right?
Also, these methods don't work at the beginning of the game, and at the end, it's generally easy to find a more or less winning tactic and win all the battles, as I think. So, the only downside of this tactic is its excessive ease, which will reduce the player's enjoyment of the game (although this depends on the player).