Does Zhonyas Hourglass's effect of saving a unit use the chain, and can you respond to it with a reaction like Gust?

Ruling: Zhonyas Hourglass uses a replacement effect which does not use the chain, so you cannot respond to it with reactions.

Nuances:

• Replacement effects happen immediately without using the chain
• You cannot respond to a unit being saved by Zhonyas with reactions like Gust