If a player uses Zenith Blade on Lee Sin to move Sett into a showdown, can they then use a limited move action to add Cithria to the battlefield?

Ruling: No, you cannot use standard action moves (including limited move actions) while inside a showdown or while a chain is resolving.

Sequence:

• Zenith Blade is used on Lee Sin as the first action of the turn
• Sett is moved into the battlefield, creating a showdown with Lee Sin
• The board enters contested state
• No limited actions can be performed anymore
• When I attack and when I defend triggers begin