Not Losing the Game Before You Lose the Game

[OneAndOnly]

Ylzma, Who Suffers in Silence -- 3BB
Legendary Creature - Vampire
Morose (Ylzma can't attack and her activated abilities can't be activated unless you lost life or a creature you control died this turn.)
Flying
If you would lose four or more life due to a single source, you gain "You don't lose the game for having zero or less life" until the beginning of your next upkeep and then lose that much life.
4/3
.
So, here's an oddity. I want Ylzma (in all her dark majesty) to work against Voltron/battleship commanders -- those who prefer to take one or two big swings to take out an opponent -- while still allowing weenies and chip damage to get through.

As I understand it, this should work with damage becoming life loss, but possibly it needs to look at damage being dealt separately from life loss. As it stands, looking ahead to see the result of an effect / ability / game action is pretty unusual. But just as obviously, it can't trigger or begin to apply after the life has been lost.

Is there a better or cleaner way of expressing this? I don't want to go full Lich / Platinum Angel treatment.

Thanks!

[Mookie]

Something I'll call out is that 'life loss from a source' isn't actually defined in the rules. There is 'damage from a source', but damage doesn't necessarily cause life loss (i.e. due to infect), and there are things that cause life loss other than damage (i.e. paying life).

I'll also check exactly what your goal is here - is it to prevent dying to commander damage, or to life loss in general? As written, it looks like causing a lethal hit causes you to still lose a bunch of life, temporarily not die, and then die on your next upkeep.

Anyway, I'll point to Delaying Shield and Forcefield as sample templates. Maybe something like 'if a source would deal 4 or more damage to you, prevent all but 3 of that damage'. Damage prevention is a white ability, but there are black ways to do this too - i.e. Angel of Suffering.

[void_nothing]

My simple expedient is just to say "As long as you've been dealt 4 or more damage by a single source this turn, you can't lose the game (for having 0 or less life) until your next turn." Although, to be really useful, the effect should really give you a full turn of being unable to lose.

Obviously, this is functionally different, but it avoids a kludge.

[OneAndOnly]

No, I'd like to make it life loss -- life loss due to game actions (ie, damage becoming loss of life), abilities of spells and effects, and payments for abilities. As written, its meant to stave off losing the game for a short duration (until your next turn) rather than prevent the game loss, or even the state that causes the game loss. It won't keep you from losing immediately due to infect / poisonous / toxic, or things like Phage the Untouchable or Vraska the Unseen, etc.