The Tenth Minikit on Green Fingers Free play

I had the same prob. Even though the arrows are telling you differently, the last canister is not in the room with giant plant you free from the cage.

You need to proceed all the way to the very end of the mission. Go to the place where Poison Ivy grows two plants, jumps on them up to a ledge, and completes the build of the elevator-cage that takes you to the final battle.

Do NOT take the cage up to the final battle!

Instead, go straight up the stairs to the right. You will come to a door you destroy with the Sonic Suit. Then use the Robin Underwater Suit to sink down to a button that opens up another tank. Step on the switch there to fill it with water and you can swim up to the final canister.

I know where it is! It's in the last room of the level I heard on someones walkthrough it's in a green room! Your Welcome!

Ok I donno how but I had that problum as well but in the area you get to by bombing the right metal fence in the first area a minikit reapered:S

Not sure if this will help. I had the same arrow pointing to the left in the poison ring room. When I continued through the level, past the pond with green light/bombs and through the gate at the left (use mad hatter or riddler to mind control the guards), there's a room with some toxic goo. At the back rght of the room, use riddler or mad hatter to get through the door. Once through the door, bomb the door (demolition suit) to your left. You will find some legos to build and use magnet suit, the minikit I was missing was on the other side of that tall wall.