[Epona]

SPOILER
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Opening the door is a piece of piss. There are 3 statues pointing towards the door (or you can push them to point to the door, just like the ones in the earlier chapter but these ones don't need locking in place), and you just know that they should blast the door away when you pull that lever, right? On all those blooming islands, the ones you teleport between by watching the arrows and pulling levers -well 3 of the islands have 2 levers, and the spare lever gets a coloured glowing light over it when you pull it, and the colour changes. Now what colour was the lightning field blocking the door? Make all the lights above the 3 spare levers glow the same colour as the lightning field, teleport your way back to the statues island by island, pull the lever behind the statues and bingo...

Yes it is a right royal pain in the arse to go through all that, the mimic's chamber has to rate as the most irritating area in the whole game!