Can a chain happen outside of the action phase, where players can play reactions (such as with Jinx Legend ability)?

Ruling: Yes, chains can happen at any time, not just during the action phase. Triggered abilities (identified by "when" or "at") can start a chain, and players can play reactions to anything that enters the chain.

Sequence:

• A triggered ability (like Jinx Legend ability) creates a chain during any phase
• Players can respond with reactions to anything entering the chain
• The chain resolves normally

Nuances:

• Playing permanents cannot be reacted to - permanents enter the chain but no one gets priority before they leave again
• Rune pool empties at the end of draw phase, which is related to chains being able to happen outside the action phase