Gates of Istfell

This is a white source that quietly holds a second identity: once the game grinds past the point where a plain land matters, it converts itself into gas. The activation is the whole design, to sacrifice it for two cards and two life, a card-advantage engine bolted onto the manabase. That cost line is careful. It demands genuine Azorius commitment (two blue pips alongside the white one), which restricts it to decks that actually want the white mana it taps for in the meantime, and the sacrifice clause means the refill costs you a land off the battlefield rather than sitting free. The lineage is old: a land that stops being a land once it has done its job, so a flood-heavy draw step becomes fuel instead of a dead card. Entering tapped is what you pay for holding that option at all. It does nothing on turn one, and it isn't meant to; the value is deferred, sitting idle in your lands until drawing two beats casting a spell.