Area 1-2 - Watchers in the Mist
Use Bandit stats from the Dungeon Master's Basic D&D, making the following changes
Challenge 1/4 (50 XP)
Remove scimitar and crossbow attack, replace with
Long Spear. Melee Weapon Attack. +3 to hit, reach 10 ft., one target. Hit: 4 (1d6+1) piercing damage.
Weighted Net. Ranged Weapon Attack. +3 to hit, range 5/10, one target. Hit: 3 (1d4+1) bludgeoning damage. If the target is a creature, it must succeed on a DC 13 Strength saving throw or be knocked prone.
Area 1-3 Fount of Filth
The strength check to pry the gems out remains the same. The curse allows the DM to elect to cause one PC to have disadvantage on a skill check (three times a day). This curse can be removed as described in the book. The XP award for destroying the altar is 75 XP to each good aligned character that takes part in the altar's destruction..
Area 1-4 Bazaar of the Bizarre
Use either Thug stats from the Dungeon Master's Basic D&D.