Norn Queen Yurei wrote:As you announce who's going Underground in the pre battle step, they count as moving once revealed, right?
Such units would count as "Reinforcements" as defined on page 208 of the rule book, unless there's some special rule in the codex making explicitly clear otherwise. When reinforcements arrive they count as having moved.
Norn Queen Yurei wrote:Also is there still a rule in place where only 50% of your army can be put in reserve/underground?
That rule is in the mission packs, for example it's in Grand Tournament 2021 in section 10 (declare reserves and transports) starting on page 5.