Just wanted to re-confirm:

His effect to inflict 500 damage does not kick in until an entire chain has resolved correct? Not for each individual card chained?

And since its a trigger effect and that the 500 damage inflicted starts a new chain...I can chain to that damage to inflict 500 more damage?

1. Correct, after the current chain resolves, Blast Asmodian will activate on a new chain as link 1. Blast Asmodian won't activate more than once on the same chain since it's a trigger effect.

2. Correct again, then it will create another chain as Chain Link 1.

Ah, thanks. I was making a burn deck and was looking at this card for awhile. I wanted to make sure it worked like I thought before running it.