What is the difference between rule 343 and 343.1 regarding focus passing after chain resolution?

Ruling: Rule 343 applies to normal chains during a showdown where focus passes after the chain resolves. Rule 343.1 is an exception for the initial chain, where the attacker retains focus after the chain resolves.

Nuances:

• The key distinguishing word is "initial" in rule 343.1
• This creates different focus-passing behavior for the first chain versus subsequent chains in a showdown