mtg card ability rules A magic corner of the Universe: Mana abilities and Caged Sun Parts of a Turn -

If you're looking for a fun go-wide Equipment deck, I'd highly recommend the Final Fantasy VII precon

Roll two d20 and ignore the lower roll

Zimone powers up when you cast a spell with X in the mana value, and then reduces the cost of X spells later by the number of counters on her

Or hey, just pay the white and four generic mana, and ultimate away one planeswalker from another ones loyalty stash

Even with myriad you're still only getting a temporary advantage, so you should make sure you either borrow something that's going to leave a mark, or lean on sacrifice effects to circumvent giving the creature back

In 2024, White has gone from having none of these 'you can have any number of them in your deck' creatures to having two