Having a look -
preps:
As a Goblin Assassin, I wouldn't recommend balanced dagger. You start with Apheelsik, situational first strike and so on, which should give you an edge on higher level enemies. You shouldn't really need to be fighting same-level monsters and, as a Goblin, you really want something like Dwarven Gauntlets or Elven Boots or whatever that gives you long-term power.
Binlor's a sound choice. The other preps are fine, with Binlor I like taking Smuggler's Den because it gives you extra blackspace to regenerate mana and walls to break for piety.
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Early game: not a huge deal but blasting an enemy into the map edge is not ideal if you want to piety farm up to 35 with Binlor. In general you're killing a lot of level 1s you don't really need to, playing a bit more carefully with pisorf would let you circumvent a bit of that. You also repeatedly blast a vampire into blackspace. Bad idea because lifesteal activates every time you reveal them.
See that Snake at 1.20ish. You could've just pushed him back along the row of walls for a load of piety and to give you a lot of room to work with up there for pisorfing other enemies. With a Binlor early game you generally want as much piety as possible so you can work towards to 65% magic resistance. At 4.50-5.00, you waste some blackspace with how you move around that vampire, use that 4 tiles of mana to, say, get some piety by pisorfing that level 9 snake. That kill on the level 7 is just the sort of thing you should be aiming for, though.
Dwarven Gauntlets a really good purchase here. Good job using Imawal throughout.
When you get yourself into that sticky situation fighting the acid blob, I think it would've been more efficient to kill some lower level enemies for the level up than blowing most of your remaining blackspace while poisoned for the 2 XP from it.
Secret subdungeon - you could've blown those four enemies around you into the corner walls for 20 piety, spend some mana getting 5 piety out of that snake topside and then used all of the rest of the dungeon's blackspace just to generate Binlor piety with Endiswal. More efficient pisorfing, grabbing the endiswal boon and more focus on gaining piety with Binlor would've helped you a lot here - I can't see exactly how much magic resistance you're going down with but I'm guessing it's well under 50, most of the walls topside are still up, and you've only got 10 piety saved up, which makes it really hard for you to use any of the other gods or stoneskins on the bottom.
Smart decision to head down just before a level-up. Helps a lot with the first wave.
First wave of bosses - two magic resistance bosses. Getting three stacks of curse from Tomithy is going to make it harder to efficiently regen fight the others - especially Aequitas, whom you could otherwise easily poison and regen-fight to death without using up that Death Protection. You can't regen-fight that wraith with fireballs - the blackspace you spent there would've been better used killing Aequitas straight off, I think.
Second wave of bosses - probably two of the three toughest opponents in one for your class. I think you'd probably have ended your run on Frank regardless. Not having piety really limits your options for dealing with them.
Mistake at 13.09. You would've saved a lot more resources by using a mana potion to cure the burn, regenerate all your stuff and then level up while you're fighting the bosses. Having two levels worth of health/mana in the fight is invaluable against these bosses.
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Anyway, not a bad run all in all and I don't mean to be discouraging. Key things are:
A) Balanced Dagger on Assassin not ideal imho.
B) Binlor piety generation and general use of pisorf could be a lot more efficient. There are tons of walls topside, so you can generally hit 40-50% magic resistance and at least 50 piety to spare before you head down without too much trouble.
C) Level-ups and blackspace are resources much the same as potions. When you see a wave, work out which bosses you should regen fight, which you'll need to spend potions or a level-up on etc.
Hope that helps, sorry if too much textwall gotta cook dinner because heading out soon but I'll answer the rest later, hopefully.