2020-04-17 : Huntmaster Liger’s triggered ability affects only creatures you control at the time it resolves. Creatures you begin to control later in the turn won’t get +X/+X.

2020-04-17 : The value of X is determined only as the triggered ability resolves. Once that happens, the value of X won’t change later in the turn even if Huntmaster Liger mutates again, although in that case the creatures will receive a second, larger +X/+X in addition to the one generated by the ability’s earlier resolution.