Being able to (potentially) cheat out cards like Worldspine Wurm, Shriekwood Devourer and Thunderfoot Baloth is nice, but there are some solid reprints, too
Retrace is another mechanic that triggers Sevinne, a job also accomplished with cards like Torrential Gearhulk
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Cards like Kokusho, the Evening Star or Erebos, Bleak-Hearted may be better alternatives that offer similar benefits without the high mana cost, making them more viable options for gameplay
She can give you oodles of mana easily, she can draw you cards, and she can synergize with many other untap effects to produce more mana than you know what to do with
Change 3 to 5 cards max per iteration, then test again