Can you activate a unit's ability (like Sett Brawler's) after using Showstopper to move it to a battlefield, or does showdown begin immediately after the move?

Ruling: You cannot activate abilities without Action or Reaction tags after moving a unit to a battlefield because a showdown begins immediately after the move is completed. Sett Brawler cannot use his ability to consume the buff from Showstopper.

Sequence:

• A move command is executed (e.g., Showstopper moves a unit to battlefield)
• The move completes
• Cleanup begins immediately
• The battlefield is staged for combat during cleanup
• Combat/showdown starts (if there is no chain)
• Abilities without Action or Reaction tags cannot be used during showdown

Nuances:

• A showdown won't begin if a chain exists, even if the unit has been moved to a battlefield
• Abilities with Action or Reaction tags (like Wallop or Call to Glory) can still be used to consume buffs because they have different timing restrictions
• The same timing restriction applies to other cards like Vi after Ride the Wind and Arena Bar