Does Shield activate immediately when Shen is summoned, or does it use the chain, allowing an opponent to Gust him before Shield takes effect?

Ruling: Shield is a passive ability that does not use the chain. Shen gains Shield (5 might) immediately when he enters the battlefield, with no response window for the opponent to Gust him.

Sequence:

• Shen is summoned to the battlefield
• A cleanup occurs
• Shen is assigned the Defender designation (because the controller has a unit at the battlefield being attacked)
• Shield goes online, giving Shen +5 might
• No reaction windows occur during this process

Nuances:

• Shield and Assault are passive abilities that are either on or off - they never trigger or use the chain
• For Fiora's trigger purposes, Shen does become mighty (through the cleanup process), but he is not mighty "as played" for purposes like Volibear
• The distinction matters because getting assigned Defender happens during cleanup, not instantly upon play