Trial of the Hydra

On the topic of Magic the Gathering again, I got the Hydra challenge deck recently, and after playing with it for a bit I've come to some flavor decisions in regards to it and an additional rule that I'm going to implement while playing.

The Hydra challenge deck has one or many players fighting cooperatively against a deck that does constant damage to all players, while simutaniously healing them should they fell any of it's heads. This eternal shift of lifeforce back and forth is very unlike any instance of damage normally used in the game's normal use (there are some instances of it, but a player is causing it to happen to themselves rather than it happening upon killing a foe), this makes me think it's not life but moral that the Hydra does damage to. As each new head grows or as each attack it deals, things become more hopeless for the players, whenever they strike down a head they would feel renewed in their actions. Thus explaining the flow of "life" and it's strange back and forth flow.

The extra rule I'm proposing is due to an instance where a player managed to consistently kill the heads of the Hydra but due to a strong start on the Hydra's behalf, couldn't finish the fight. What they could do was gain life. And by the time we decided it would not be worth continuing, they were gaining 17 life a turn and killing a single hydra head, they had 104 life when we stopped, and as such I propose an additional victory condition:
The Shonen Rule - If a player has more than 100 life at the end of the Hydra's turn they win the game
This is because I see the Hydra fight as less against the Hydra, and more a battle of the players overcoming their own weaknesses, so if they reach 100 life, they have reached a point where they can believe in themselves such that they can accomplish anything as a plainswalker and as a hero (there's a large amount of  hero messages in the set the Hydra challenge deck is set in, the reason to be a hero and the journey of one from person with strength to a warrior worthy of their legend) 

P.S. it's called shonen rule cause of the prevelance of such a trope in shonen manga like Naruto and Bleach where if the protagonist believes in the,selves enough they are unbeatable