Can you play Cull the Weak (a basic spell with no action or reaction keywords) during a showdown after a unit is moved into a battlefield?

Ruling: Cull the Weak cannot be played during a showdown. It must be played during the action phase on a player's turn when the game state is open (no chain active).

Sequence:

• Must be played during action phase
• Must be on the player's turn
• Game state must be open (no chain)

Nuances:

• Basic spells without action or reaction keywords cannot be played during showdowns