Haunted Cemeteries: Run those when you have time as it gives you plague poison, a poison that sacrifices damage for a massive range. It’s not necessary but it’s definitely a fun poison, one of the poisons that was almost not buffed at all during the massive poison update. It’s a solid, especially when trying to hit things you can’t even see.
Sewers: Murky Toxin is the highest damage poison. In exchange for being more difficult to land, it offers a total of 1,200 damage for 120 MP relative to the 900 damage for 100 MP from a baneserpant.
Puppet Master’s Theatre: Good ol’ harle. The resu for hide classes, offering a decent amount of MP at the sacrifice of defense. Great for assassin as assassin is ability based.
Shatters: GEMSTONE. Gemstone is the classic MP ring, although as of more recently, it is arguably outclassed by the Sourcestone from Lost Halls. Both rings are rare to get but given that there’s a shatter event going on right now, you may want to try to get a gemstone right about now because those things are hard to get.
Lost Halls: As mentioned above, it drops a magnificent ring called sourcestone. Additionally, it drops the longest ranged dagger, something that may work well with the natural long range of the assassin’s ability.
TIERED ARMORS AND OTHER SMALL THINGS THAT MAY HELP:
Keep a tiered dagger: t12 (dagger of foul malevolence), t13 (dagger of sinister deeds (SB))
T6 poison (baneserpent) is never a bad choice
Keep a tiered armor for defense purposes t13 (Hydra), t14 (Wyrmhide) or csilk (from OT) or behemoth armor (from Nest)
Keep a survival ring (UBHP, Decade, Pyra, Bracer)
ST assasin set is also nice but I know nothing about it because I quit temporarily at around the release of it and don’t care about it