Test of the Smoking Eye is intended for four 10th level characters, but it can be modified for parties of different sizes or levels. Consider adapting the adventure as follows:
Reduce the number of babau demons at the start of the adventure by one. While the PCs journey through Occipitus, add 50 to any rolls made to generate a random encounter; rolls in excess of 100 should be treated as a result of 100. In the Cathedral of Feathers, remove either Liuvash or Arrokh from the Sanctuary, and make the North Chamber where the bebilith lurks a less complex room by removing the bridges and setting the floor of the chamber at the same level as the doors. On the Plain of Cysts, remove the encounter with the Abyssal Basilisk and reduce the class levels of the Wee Jas grave robbers by 1-2 each. Vorkaire should be changed to a young adult black dragon. In the Skull, replace Motruk with a Chaotic Evil stone giant, lower Myaruks thaumaturgist level by 1-2 and remove the negative energy damage effect from the nexus, and lower Kaurophons level by 1-2.
Add an additional babau demon to the start of the adventure. While the PCs journey through Occipitus, subtract 50 from any rolls made to generate a random encounter; rolls lower than 1 should be treated as a result of 1. In the Cathedral of Feathers, add 1-2 more driders to the Narthex, give both Liuvash and Arrokh 1-2 levels of fighter, and advance the bebilith in the North Chamber by 2-4 Hit Dice. On the Plain of Cysts, have the PCs encounter an abyssal basilisk twice, advance the retrieer by 4-8 Hit Dice, and add 1-2 class levels to each of the Wee Jas grave robbers. Give Vorkaire the fiendish template or advance him by 1-2 Hit Dice. In the Skull, add a pair of vrock minions to the encounter with Zaur Sza and Motruk, advance the berserk clay golem in the throne room by 4-8 Hit Dice, and give Myaruk and Kaurophon 1-2 more class levels. If youre feeling particularly mean (or if your players are still waltzing through the adventure) you can have the various mummy lords that the PCs encounter attack them after they complete a part of the test as a final stage to each test.