I think there was a help tip about some movement skills being able to grant each character movement in a turn, and I'm pretty sure I've seen the AI in campaign move multiple critters within one turn, but I can't for the life of me figure it out. Thanks much.
Also, Gary can move a whole minion group with a standard move card. This does not apply to normal players.
AI opponents that share a card pool also share the use of movement cards; That's why it may seem like multiple move at once. Players or solo AI's that move with others though may be doing it via a card effect like what skip_intro posted.