When this tactic resolves, can I use the action the card lists once, or can I use the action once upon resolution, and then X number of times in response to the initial action with X being the number of available uncorrupted Skaven units I control? More generally, is the resolution of this tactic considered the "trigger" for this action, causing me to corrupt a single Skaven to activate the action, or does the printed action not have/require a trigger?

Further, has there been any word on whether the lack of the Skaven trait on this card was intentionally or an error? Important to know for other Skaven cards like Chittering Horde and Greyseer's Lair. Same question applies to Manfried's lack of Hero trait.

Thanks!

When you play the tactic, you pay its cost and choose the target. The cost is two resources and the corruption of a Skaven unit you control (see the FAQ, Terminology Clarifications, Triggering a Card Effect, when a card says do X to do Y, do X is a cost). The target is your opponent. Then you and your opponent might add additional actions to the chain. Once the tactic resolves, you count the total number of corrupted Skaven units under your control, and deal that much indirect damage to your opponent. You may not corrupt additional units during the resolution, or deal several amounts of damage. You may add another copy of the tactic to the chain in response to your playing of the first copy, provided you can pay its cost too, but you can't respond to the tactic with itself.

I think it obviously should have had the Skaven trait, but don't hold your breath for an errata. It seems traits aren't considered so important they get errata, not even the "Calvary" typos have been corrected yet.

Unless there is an errata released, the card isn't considered a Skaven card. And like Mallumo said, don't hold your breath on errata. Lukas saves errata for stuff that is pretty clearly wrong or broken.