Omnath, Locus of All

If you would lose unspent mana, that mana becomes black instead.
At the beginning of your first main phase, look at the top card of your library. You may reveal that card if it has three or more colored mana symbols in its mana cost. If you do, add three mana in any combination of its colors and put it into your hand. If you don't reveal it, put it into your hand.

Seedborn Muse

Untap all permanents you control during each other player's untap step.

Doubling Cube

{3}, {T}: Double the amount of each type of unspent mana you have.

Nyxbloom Ancient

Trample
If you tap a permanent for mana, it produces three times as much of that mana instead.