Dragon's Rage
Move an enemy unit. Then do this: Choose another enemy unit at its destination. They deal damage equal to their Mights to each other
That "do this" wording (or similar) tells you that what follows is a separate instruction from the original. As you start to play Dragon's Rage, you only need to choose an enemy unit and a battlefield to move it to. Then, assuming Dragon's Rage resolves, you'll put a separate triggered ability on the chain, choosing another enemy unit at its destination (if one is available). That triggered ability can then be responded to separately. If there's no enemy there, or if you didn't actually move the unit you chose for any reason (and therefore there's no "its destination" to reference), the trigger isn't put on the chain at all.
This isn't a tool we expect to use often, but it lets us make sure that cards like Dragon's Rage offer chances for interaction and decision at points that feel appropriate.