Is 'when I move' considered an ability that creates a chain and gives the opponent an opportunity to react, such as when moving a Merchant from a battlefield to your base?

Ruling: Yes, 'when I move' is a triggered ability that is placed on the chain, giving the opponent an opportunity to react when a unit like Merchant moves from one battlefield to your base.

Nuances:

• Triggered abilities wait for something to happen and then do something, and they create chains
• Activated abilities (those you choose to activate by paying a cost) also create chains
• You cannot respond to a unit being played itself, only to abilities that play a unit or abilities that unit has that trigger when it's played