Stampede and The Grim Roper

[krenopus]

The Good, The Bad, The Munchkin

Q: 4 player game. Player kicks in the door and finds a low point monster.
(this fight is for the win).

So, I play the Stampede with the Grim Roper.

Does the Grim Roper close the Stampede?

Or can everyone else at the table add monsters to the stampede?

Paraphrasing (cause I can't find the cards to link)
Stampede: each player at the table may add a monster to the combat.

The Grim Roper: no other cards may be played to affect the combat.

Thanks!
Kren