Spirit of Obligation

Players may pay an additional {1} as they cast
spells.
Whenever a player casts a spell, if it wasn't taxed,
they lose 1 life and you gain 1 life. (A spell is taxed
when an effect causes its controller to pay additional
mana as it's cast or when an effect targeting it causes
its controller to pay mana.)
You'll pay one way or another.