Recently, I was discussing a couple of combinations when this one came up. Fellblade says that the attached card deals X more damage while in combat where X is the number of resource tokens on it. My take on this is that when attached to a Night Runner, after the Night Runner is assigned to attack, the Fellblade would add to the indirect damage he deals because at that point he is dealing damage while in combat.

Am I reading the card combinations accurately?

It wouldn't add to any indirect damage at all. It would just add to combat damage

A warp lightning cannon would work because it adds to his power while attacking and defending. Thus, his power is 4 while attacking or defending then pop off an indirect shot of four. Felblade is extra damage and never actually adds "power".

so played a game last night and this came up -

Night Runners w/ Warp Lightning Cannon attacking. he corrupts to deal his indirect damage of 4 after being declared. 1 unit defending. Chillwind to corrupt that unit in response & uncorrupt Night Runners. They deal their 4 combat damage unblocked, then corrupt to deal 4 more indirect damage .