Planar Ally

Most dungeon-crawlers paid their entry once and moved on; this angel walks a room deeper every time it turns sideways, converting a single permanent into a recurring crawl for as long as it survives. The trick sits in the trigger condition: it keys off the attack declaration, not combat damage, so a wall in the way or a defender who eats the swing never stalls the dungeon. Declare the swing and the room advances regardless of what happens after blocks. That folds the venture into the combat step rather than the main phase, so the crawl progresses on the same turns the game is already moving forward. The 3/3 flying frame carries the tension: evasive enough to keep threatening a cluttered board, soft enough that a single removal spell shutters the engine before the deeper rooms pay off. Which dungeon you walk changes what the identical trigger is worth, since a shorter path banks a modest reward quickly while a longer one commits to a bigger finish across more attacks. It is a repeatable-value creature built for a mechanic that rewarded density: stack multiple venture sources and the dungeon closes faster, and this one keeps the count ticking up for the price of showing up in combat each turn.