Can you play a reaction spell like Shakedown during a showdown chain when moving Watchful Sentry to an empty Trifarian War Camp (where no combat occurs)?

Ruling: Yes, you can play reaction spells during a showdown even when there is no combat. Both players get an opportunity to play spells (action and reaction speed) during any showdown, which only ends once both players have passed on an empty chain.

Nuances:

• The showdown chain exists regardless of whether combat actually occurs
• Both action speed and reaction speed spells can be played during the showdown