There are countless cards that let you trade life for other resources, and Bolass Citadel is one of the most (in)famous
Additionally, if your opponent has a heavily damaged Pokemon on the Bench, you can bring it forward for an easy Prize Card
It does other things, but thats the ability you want
BPhillipYork: Flashback effectively being pasted onto all your spells is really solid
While Martyr + [casthaven]Proclamation of Rebirth[/casthaven] is the engine to a more controlling build of Soul Sisters, here it is sacrifice this to turn on [casthaven]Serra Ascendant[/casthaven] or make target burn player cry. Its the most all-in card in this list and while it does synergize well with multiple cards in the deck, its the first thing I would cut if there were no budget considerations
That's massive ramping, but it costs seven, but in a color that ramps lands not mana rocks, that could be a lot of value and seems doable