Merry's Sword is used as a maneuver action (not a skirmish action). The phrase "you spot" (as opposed to "you can spot") means you can choose however many
![Rohan [Rohan]](https://lotrtcgdb.com/forums/Smileys/classic/rohan.png)
companions you want to spot, but then you must take the action of exerting a minion that many times. The "for each" part means you can spread these exertions however you like, including exerting a minion more than once.
It's useful against
Enquea LoM when more than 5 companions are in play, and in
![Rohan [Rohan]](https://lotrtcgdb.com/forums/Smileys/classic/rohan.png)
wounding decks. One tactic is to run it with
Swordthain and
Sword Rack;
Swordthain bounces himself back into your hand, restoring his vitality, and
Sword Rack stacks the Sword (which would be discarded otherwise when Merry bounces) for later use.