What are legal targets for Red Rumble Discard on Conq?

Rumble, Hotheaded's conquer ability doesn't use discard — it says "recycle another friendly unit." Those are two different game actions. Here's what's a legal target for that recycle choice:

Legal targets: Any friendly unit you control on the board (your Base or a Battlefield) that is not Rumble itself. This includes token units (FAQ #3009, #8409).

Illegal targets: Units in your hand, your trash, or anywhere off the board — the term "unit" without qualification only refers to permanents on the board (FAQ #3053). Opponent's units are also invalid since it says "friendly."

The recycle is a targeted choice — the unit you recycle is chosen when the ability is finalized on the Chain (Rules 355.10, 355.12). Its Might is checked at resolution to determine the cost reduction for the Mech you then play from your trash.

Important distinction: There's no discard involved here at all. The unit you recycle goes to the bottom of your Main Deck (or vanishes if it's a token), not to your trash.