Is discover-discover legal in a way that it actually is productive? Is it effectively burst two and the only way to fail changing their marker state (to marker if CH or to IMP-2 if impersation) is to fail both of the now B2 discover? If not legal, why?
Yes, you can declare Discover-Discover, either on the same target twice or on two different targets. It would be sort of like a Burst 2 Discover, yeah... So long as you keep in mind (as you mention) no matter if you roll one or two successes you would only remove one layer of Impersonation at a time.
Correct, IMP can only lose 1 layer at a time regardless if this is legal or not, or even coordinate order discover (or if discover-discover in a coordinate order is legal), but the -6 is a significant mod and its not like you are going anywhere till their dead.
If you pass 1 roll but fail the other, you're still unable to discover any further on that target I believe though (for impersonation).
If you succeed and fail, you cannot continue on that marker, however they have changed markers and so arent the same as what you failed against.
It's basically the same reason why you can't peel off more than one IMP layer per order; the IMP-1 Marker is not the same Marker as the IMP-2 Marker.
Sorry to disappoint you, but.. A trooper that fails a WIP Roll to Discover a Marker cannot attempt to Discover the same Marker until the next Player Turn. The trooper may still attempt to Discover a different Marker that Player Turn, and its player may still attempt to Discover the first Marker using a different trooper. So, you can declare Discover + Discover, but there's little to no reason to that: If you fail the 1st Discover, you cannot attempt another one against the same model until your next turn. You can try to Discover another model with that 2nd Discover, but.. Many players will just declare a Surprise Shot ARO against you after you declare Discover as your 1st Short Skill, because there is little reason not to. Now, if you spend your second Short Skill to Discover, you're basically forfeiting any chance to do anything to enemy model. You can declare Discover + BS Attack, however. Moreso, you can split the Burst between the model you're trying to Discover and some other target, losing shots against the marker if you fail the Discover roll.
There is no sequential nature to the rolls in the resolution stage, you don't roll one discover then the next, you roll both at the same time, so neither is invalid at the time of declaration or rolling. That rule you referenced prevents you from attempting discover with the same trooper, on the same marker, in the same turn, on a subsequent order if you have already tried and failed. Surprise Shot is not a valid ARO, I'd politely tell your opponents that they meant BS attack instead (much like I don't sweat the difference between Dodge and Change Facing on declaration). Your opponent has to declare his ARO before you declare your second short skill; if he reveals the marker, a second discover is invalid, so you could never declare two discovers against the same target if it reveals after the first.
