I love these games
How to get past the pool in the cave glitch:
It only occurs after you click on the pool and try to move. If you throw the gelatin in the pool and then switch to Reemus, you can use Reemus to move Liam out of the way and avoid the glitch. Just click on the pool with Reemus, and click somewhere else immediately after Liam starts to move. That way, Reemus won't get stuck in the same place.
How to get the Passion of the Exterminator medal:
You basically have to complete both the Reemus task and the Liam task in the first area. Once Liam lets the Roach go, Reemus will still have the axe in the next area which he can use on the Roach.
I also encountered a glitch in the last Liam level, by the shore. When I tried to reset the level, the SWF warped so that it was half of its normal width, occupying the left half of the Flash window. I had limited interactivy, being able to switch characters and move a little but not being able to leave the screen or really do anything. Since I couldn't reset the level, I had to refresh the window and all my progress was lost.