As their followers are compleated, it starts affecting the gods
On the other hand, if untapping multiple permanents is part of a cost (such as that of Halo Fountain's last two abilities), you can't "untap" the same permanent more than once to pay that cost
A lot of that is thanks to Zurgo Stormrender, a three-mana creature that creates tokens but lets you either draw cards or drain your opponents whenever a creature token you control leaves the battlefield
Likely, this will be Player Y's or Player Z's
However, rather than countering Brainstorm decks, those are the same decks that are playing it, and part of why the Dimir shell is so powerful in Legacy
Regardless of which commader you play, the unearth cards and graveyard recursion makes the deck incredibly resielnt and hard to keep down