Note: It is not possible to go back through Mogall Forest. However, it still is possible to make your way through Mogall Forest without Force (just follow the directions to go in this walkthrough.)
No, not Muggles from Harry Pottery but Mogall. Here you'll see a green monster climb into a tree. Use force on this tree to see the Djinn run out to the south. On this screen you'll see another big stump, but you don't want to use force on this or you'll have to fight an Ape. Push the vertical log to your right, the horizontal log down, the vertical log back to the left, and then the horizontal log up. This will land the horizontal log in the water and you should jump across it. Use Force on the stump you're now next to in order to see the monster escape the east. Follow him! Use Force on the western most stump to see that pesky monster run south, so yet again follow him. On this screen head east to arrive at a horizontal log that's being constricted from moving due to a rock. Use your Move Psynergy on this rock to push it in a hole and move the horizontal rock down. Roll the next horizontal log in your way down, then move the vertical log to the right. Move the horizontal log all the way up, then once again move the vertical log west into the water. Before you hop over to the next part, go to the southwest part of the grass section you're currently on to find a Djinn! Save before you fight this guy, because you'll need to battle him. He's not very tough to beat, so you don't need to worry too much as long as you have your Djinn inactive before hand to hit him with summons. Now, hop across the log and use Force on the stump there. The monster will jump across the island gap, but you won't be able to jump across that. So, head back from whence you came (9 I think) to the northern part of the screen. Walk across the log path that was already there, and go through some trees to arrive at the big stump. Force on the stump to have the monster run off to the west. Follow him and go through the screen going west. You'll now arrive at a place with three stumps. Here you'll want to use Force on the middle screen to have the monster run south. Head west and then down the log over water path there. You'll see a vertical log blocked by a rock here, so use Move to move the rock into the hole. Once you've done this, push the vertical log right and jump across the water to the island in the middle. Use force on this stump to have the monster jump across to the water to the south. Jump back across to the west and head around the mini-stumps counter clockwise. Push the vertical log east, then the horizontal log south. Head around counter clockwise again and push the vertical log east into the water. Save before you hop across this log, because you're about to get a boss battle. Use your Force Psynergy once again to force the monster out of the stump and to the south. Follow him and make your way towards the stump in the middle on the next screen. When you walk towards the log in the center you'll see the monster jump to the south. Follow him, but get ready for his BIG counterpart to ambush you.
It's now time for a boss battle against Killer Ape. This guy has a lot of health, and his attacks aren't too shabby. The first thing you want to do is cast all of your summons against him to do a good deal of damage (by now you should have at least one 3-Summon) to him. Now, Isaac should also have a nice new attack called Ragnarok that packs a huge wallop (it's my favorite looking attack in the game.) Have Garret use his normal attack (I equipped that Arctic Blade on him that I liked pretty much for this point in the game), use Ivan's Plasma and occasionally Impact on Isaac, and keep using Ply with Mia to keep your other party members alive. When you beat this Ape you'll get 1500 coins and Douse Drop that's required much later in the game. Head south once more to find yourself out of Mogall forest. Note: You can't go back through Mogall forest no matter how hard your try.
Head east and go north over a bridge to reach Xian.