It's been a few months since the last one, and since Assassin is still rather lackluster both in terms of flavor and at actually assassinating anything, I thought I'd raise this topic again.
Going to go straight into the meat and bones of it - here are a few great suggestions for improving Assassin:
1) HIPS at Level 8. A common suggestion with a lot of history. The drawbacks are also well-known to those who remember the earlier threads: there are fears giving Assassin HIPS might dilute the uniqueness of classes like Shadowdancer. Personally, I think this is something that can be resolved. After all, in pen and paper, Assassin does have Hide in Plain Sight at Level 8. I think it would make a lot of sense to at least give them this.
2) Crafting poisons / ways to improve the DCs of existing poisons. This would require creating new poison items, I believe, or adding in existing poisons (with bumped-up DCs) as Assassin-unique items. Since poisons are a part of the Assassin's toolkit, this would be a flavorful mechanic to add to the class which would make the class more unique, allowing it to stand out from your standard rogue/fighter/rangers and whatnot.
3) Add more Assassin-specific trinkets and equipment. Currently, there are very few such items in the module, and there could stand to be a few more - these items should mainly concern spell slots, as otherwise other UMD classes might benefit too much from them.