If a unit moves to an unoccupied battlefield and casts Cleave, does it get +3 attack since there are no defenders?

Ruling: No, the unit does not get +3 attack when casting Cleave on an unoccupied battlefield because without defenders present, it does not count as attacking.

Nuances:

• The Assault 3 keyword lasts until the end of the turn
• If an opposing unit is moved in during the showdown, a combat is staged and the unit retains its attacker status from the first showdown, gaining the +3 bonus during that combat
• Multiple instances of Assault stack (e.g., two Cleaves would grant Assault 6)