I'm pretty sure CotW nerfed Grease. It was close to useless the few times I tried it with the mod.
The nerf was kind of necessary, to be fair.
I'm playing CoTW. I am now only 5th level, so I cannot say how it works on the higher levels. But for me, so far, it worked for all the difficult fights with big-HD enemies. Even the Champions. Only the Wererats with very high reflex-saves begged to differ -.- All other fights, inc. Owlbear fight at the Stag Lord's, enemies get hopelessly stuck if I cast 1-3 greases under them and, for the added safety measure, Entangle. The Wand of Grease helps too.
Idk how it was supposed to (not) work, but the enemies generaly fall prone almost every turn after a single step. When they reach my front liners standing at the very precipice of the grease, after the many turns of being bombarded by the archer / bomb / spell squad issuing all the ranged mayhem possible, the tougher enemies have like 1/2 or less HP. Once the enemy falls prone before the 1-3 frontliners and then stand up again, they generally receive a tremendous damage, mostly getting killed due to those 1-3 free attack of opportunity.
The same went on in the fight at the Stag Lord's. It was very intense, almost as if from some fantasy book. Four of my characters were unconsciouss. What remained was two archers depleted in health, scrolls and wands in their last stand, hudled at the end of one of the two wooden plateaus. Also there was a lone cleric at the far side of the entangled ground, unable to engage. Now, the Owlbear being the last enemy alive, still with half of his tremendous HP pool, crawled slowly through the entangled effect towards the two archers, falling prone every odd turn or so due to the many Grease spells. Nevertheless, it was steadily, ominiously closing in. Tough-as-nails, arrows kiting it to some extend, but never very much. In the very end it climbed the wooden stairs, freeing itself from the slowing spells, and made it close enough to almost claw at the archers. Though the Owlbear was almost out of HP at that time, it would had taken only one more turn before the archers would be finished. That one fatal turn however, cleric also got in reach from the other side. He's tossed the last saved Alchemist's Fire, and has actually killed the monster. Was a helluva lucky lob. Cleric dexterity 10, only one bottle of fire left, the monster probably with 10-20 HP left or so. It took me totally by surprise, and I wtf'ed my screen wet :D 15 mins of a turn-based fight! Couldn't believe it ended in win and in such a way. I didn't even check the combat log at that time.
Btw, looked later at
https://www.d20pfsrd.com/equipment/weapons/alchemical-weapons/ I now know, the Alchemist's fire can crit. So it must've been one - a top of the roll at that.