For sustained mana, Cabal Coffers works best in mono-black, though it can be used in other color combinations thanks to Urborg, Tomb of Yawgmoth, though those decks make this a weak half of a 2-card combo
13: Mana Drain Its pretty amazing that Mana Drain, one of the most broken cards ever doesnt crack the top ten, but this is a high-powered eternal format, which means a vast majority of cards people play are very cheap
Yes, it costs 6 mana, but most good sweepers are in that mana value range, and this cards effects are probably the best you can get for it
Either way, there's no doubt that this will be played quite a lot
Though not new to Magic: The Gathering (you can check out our guide on how to use double-sided cards here), double-sided or double-faced cards have not been featured in a Modern Horizons set before