Hoi,
Now that Defend The Main Room is an active quest again I figured I'd post this quick guide for newer players. It's a generally safe, consistent farm of 3 Ill Gills every 2 mins or so.
In a perfect run the Gi Gue will leave you alone and the final Del Lily will trigger mag as a response to your barta first try but I decided to show one where things don't go according to plan. Keep the Gi Gue in view so you can tell if it's countering. So long as you run straight and slightly to the left when warping into the room you should be fine. Your mag might trigger during the first part when you're killing the other plants but it will most likely run out before you can wipe out the Ill Gills so best to let it time out then reactivate as per the video.
Happy hunting