The next issue with 1.9.0 on startup after updating Astral Sorcery from 1.8.10. Perhaps a duplicate of #746 #747 #748 #749 #750 #751 ?

The Problem: Client crashes on startup.

The crashlog indicates SlimeKnights mods to be the problem, but after removing one by one of the Tinkers Cosntruct Addons and at least Tinkers itself (not Mantle) , the new crashlog indicates IC2 as the problem. And at this point I've decided to go to the issue tracker. ;)

Forge 14.23.4.2708
Astral Sorcery 1.9.0
Tinkers Construct 2.10.1.87
Mantle 1.3.2.24
Constructs Armory 0.0.23-rc3
Plustic 6.5.2.0
TAIGA 1.3.2
Tinker I/O 2.6.1
Tinkers Completement 0.2.3b
Tinkers Tool Leveling 1.0.5
IndustrialCraft 2.2.8.84-ex112

Should probably open tickets on those mod's trackers, tbh.

Edit:
Actually...check with "noppes.npcs", looks like a common source for the issue.

Confirmed. After removing Custom NPC's (13may18) the client starts with AS 1.9.0.
But I need it for my quest-modpack, therefore I'll stay on AS 1.8.10 until a fix is out.

You need to open a ticket on the Custom NPCs github, or they won't be able to figure out what's going on and fix it.

Already done. I opened a ticket on their curse issue tracker. :)