811.1.d.1.a. This includes hidden gear, and overrides the normal restriction that gear have in only being allowed to be played to base. This core rule specifically mentions that a gear must be played to the BF, ignoring its original restriction. But then when the gear is played, it will be sent back to the base during a cleanup anyway since another rule says that a gear not being equipped to a unit cannot exist in a BF. Then what’s the point of the whole special mention and seemingly superseding rule?

The gear is not recalled instantly — it stays at that battlefield until the next Cleanup (Rule 457.1, 149.3). That window is exactly the point.

First, the special mention in 811.1.d.1.a exists to resolve a rules conflict, not to create a lasting state. Playing from Hidden requires the permanent to enter at the battlefield where it was hidden (811.1.d.1), but Gear intrinsically "can only be played to a player's Base" (149.2). Without the override, playing a hidden gear would simply be illegal — the Hidden rule and the Gear rule would both be mandatory and contradictory. The recall rule (149.3/457.1) is a delayed corrective action that happens at the next Cleanup; it doesn't negate the entry location.

Second, a Cleanup can't run while items are on the chain — it's queued as an Outstanding Task (Rules 319, 321). So a hidden gear played as a Reaction enters at that battlefield and stays live there for the entire chain (and beyond). That's when its job gets done:

• Zhonya's Hourglass: play from facedown for [0] as a Reaction when a friendly unit there would die — it enters at the battlefield and its replacement effect kills itself to save the unit (FAQ #1663). It's consumed before any cleanup ever sees it.
• Edge of Night: its play effect attaches it to "a unit you control (here)" — it enters at the battlefield and immediately attaches to a unit there. Once attached it's no longer "unattached," so the recall rules never apply and it stays on the unit indefinitely.

The one genuine wrinkle: the "corrective action" wording in 149.3 reads like an immediate recall, but that's a known rulebook contradiction — the intended timing is recall at the next Cleanup (FAQ #4849). So the gear isn't shuttled back the moment it hits the board; it serves its purpose at the battlefield first.