Bottomless Pool // Locker Room

The Room mechanic's whole trick is deferred payment, and this card splits its two doors along a clean tempo axis. The cheap side, Bottomless Pool, is a one-mana bounce that resolves when you cast it: casting a Room half enters it with that door unlocked, so the return-a-creature trigger fires on resolution, all at sorcery speed since this is an enchantment with no flash. What makes it structurally distinct is not deferral on the first door but persistence: that door stays unlocked on the battlefield, and the second half waits there as a latent upgrade you can buy into later. The expensive side, Locker Room, is a repeatable draw engine keyed to creatures connecting, and because it triggers on "one or more creatures" (a single draw no matter how many attackers land in a given combat damage step), it rewards a steady stream of unblocked damage without spiraling on a wide board. The real hook is that the sorcery-speed unlock clause lets you pay the second door's full printed cost off the same permanent, converting an early bounce spell into a mid-game card-advantage source without spending a second card from hand. It answers the same question Fire // Ice and its kin posed decades ago, one card carrying two modes, but where a split card resolves and leaves, both of these halves stack on the battlefield: the first door you unlock stays put and holds the door for the second.