The Rootgrave

You go down from The Mireheart near its southern entrance (8,13). It's a small level with one concrete payoff: the crimson roots running through the swamp feed here – one of the four Tentacle Roots sits in the west (3,12). Destroy all four Tentacle Roots before the boss fight and The Thing in the Mireheart goes into it weakened. The game tells you, too – with the last root destroyed you feel some dark power has faded away.

Plan for the fights. Swamplings hold the western part (2,11), and a Tentacle burrowed in the water (9,17) rises when you hit the Tentacle Root beside it. The grate with the chain button in the north (4,3) opens the way through, but it also opens the two side cages, and each one holds two Wrathspinners (6,5). Don't pull it straight after another fight.

Four skull buttons stand in the eastern part (12,7), and each one toggles a different set of the four grates to the east. From the start only the first grate is open. Press both of the western buttons and the way further east opens up.

The fourth Tentacle Root sits behind the last grate (17,8). Get to it first, because the second half of the puzzle locks it away: once all four grates are closed, the secret wall in the south corridor slides open (15,12), revealing a secret alcove with two Potions of Cure Poison, a Potion of Resurrection and a Mindwell Elixir (18,12).

So do it in two passes. Use the buttons to reach the last root and destroy it, then use them again to close all four grates for the secret wall. Check what changed after every single press – otherwise you won't work out which button belongs to which grate.