Amy casts her spell at the Beast, commanding it to return to its own plane, but nothing happens... Meanwhile, Corlon and Garret boogey their asses into the room with you, the Beast close behind.
Fortunately for all of you, three things happen.
First, a patch of grease appears in front of the Beast, causing it to loose its balance and start waving its arms around in an attempt to stabilize itself, loosing its forward momentum.
Secondly, Golem rushes forwards, slamming into the Beast with a roar of rage
And finally, two walls of force appear between the group and the two battling Behemoths.
Golem turns his massive stone head and says "Do not worry about me, I'll keep him from following.", then grabs the Beast in a massive bear-hug. It thrashes around, unable to break free, and starts butting its head ineffectively against the Golem, it's tail lashing around and smashing everything within ten feet, though it can't hurt Golem.