Im partial to Nissa, Steward of Elements, originally printed in Amonkhet
With Insidious Roots decks being a beloved albeit niche player, just about every flavor utilizes this card
That is fast for this kind of product
Many of the best competitive moves are 'TRs' rather than TMs this time around, the one-time-use TRs are only available as rewards from various places, including primarily max raid battles
It gets out of hand fast and often enables turns where you're casting four or five spells in a row
Others, like blacks relationship with mana acceleration, have undergone a surprising amount of change in terms of how many cards they receive with the ability to generate extra black mana and how comparatively restrictive they are versus a card like Dark Ritual, one of the first and strongest go-tos for mana acceleration during Magics early years