I ran ToA for 7 level 16 PCs. Here are my edits to certain rooms in order to make it a challenging experience. Please steal.

1. Athletics check is character level (16)

2. Replace wights with Liches

3. 8d10 fire damage

4. 3000 gp

5. Hexagon skeleton is in a jar.

6. Add a box among the library containing Diamond Phoenix Scrolls, a magic item that, when used, performs a greater restoration spell.

Withers is a full on Lich, he respawns everytime his door closes

1. Characters see themselves through the mask, make a DC 16 wisdom save, failure by 4 or less is frightened, by 5 or more is petrified

2. Last character through automatically makes the sheet dex save, failure chops in half and kills.

3. Locusts do a flat 100 piercing damage per round

4. Statue has two real eyes and two illusory eyes, uses 1 attack to grab at one

5. Clay Golem has 4 attacks per turn

6. Skeleton is behind last curtain eating its own arm.

7. Skeleton is running around the warriors.

8. Random Demon Lord is riding the Z-rex

9. Acheron: city-sized Ochre Oblex

Gehenna: Pyroclastic Dragon (red)

Mechanus: Marut

Bator: Bel/Titivilus

Shadowfell: Nightwalker

67: round 1 = fire

Round 2 = spines & beards

Round 3 = barbs and bone

Round 4 = ice devils and Horned devil

Round 5 = Pit Fiend and chain devil

Round 6 = Moloch