Playing Chaos: I have a Dire Mutation attached to my opponent's unit which is currently in his HQ.

It reads:Forced Intterupt: When attached unit exhausts, deal it 1 damage.

If we both commit our warlords to the same planet, that unit is coming with his warlord. A few things are happening here, simultaneously - I believe:

1)The unit must exhaust when it commits to the planet from HQ, triggering Dire Mutation's ability.

2) My warlord, Zarathur, has also comiited and his ability allows me to assign an extra damage to any enemy unit that is having damage assigned to it at this planet.

So in what order do these effects trigger, or do they happen at the same time?

My gut says I deal the unit 2 damage instead of 1 but just wanted some clarification.

Thanks!

In your scenario, the Forced Interrupt on Dire Mutation will always go first.

Forced Interrupts always take precedence over regular Interrupts to the same triggering condition (RRG, p. 7). But in your scenario, there is no triggering condition for Zarathur's Interrupt (assigning damage) until after Dire Mutation triggers. Dire Mutation is triggered first when the card exhausts, and THEN Zarathur triggers (or, at least, can be triggered) when Dire Mutation triggers.

So I was thinking along the correct lines, after all. 2 damage - take that Space Marines!

A related question:

Can a card have multiple Attachments that are the very exact same? (for example, using the example in this thread... can a unit have multiple Dire Mutation cards assigned/attached to it?)

Thanks.

Yes - you can have multiple copies of an attachment on a unit, as long as they're not "unique" cards. (RRG pg 3).

Or it doesn't say something like Limit one per unit.