A few weeks ago I was at a Modern cash tournament and watched as a Jund deck, up multiple threats (including Kroxa) and cards against Bant Snow just lose to Uro, Titan of Nature's Wrath recursion because Jund couldn't dig for Scavenging Ooze
Hall of the Bandit Lord and Hanweir Battlements grant haste too, but they cannot produce red mana
Hellbent If you have no cards in hand, instead search your library for a card, put it into your hand, then shuffle your library
Mana ramp cards like Rampant Growth and Knight of the White Orchid, mana rocks like Worn Powerstone and Sol Ring, tutors like Idyllic Tutor, Demonic Tutor, or Imperial Recruiter, recursion spells like Eternal Witness and Argivian Find, and card drawing/filtering spells like Rhystic Study, Dig Through Time, Wheel of Fortune, and Faithless Looting can all be cards that fit within this category
Legion Loyalty copies anything from tokens to legendary creatures
Inspired by the legendary Black Lotus, it can generate three mana of a single color, but it can only be used to cast the commander