Grease is flammable (From Sage Advice, JC states it is not)
I mean, if we're talking about differences between BG3 and the PHB, which is the title of this thread, then this one doesn't count. The PHB absolutely does not say that Grease isn't flammable, it historically has always been flammable, and many people disagree with the Sage Advice. If I had to guess, between the DMs that don't know/care about Sage Advice and the ones who think this particular one is wrong, I'd venture that at least 3/4 of tabletop 5e games play with flammable Grease.
Jeremy Crawford @JeremyECrawford If the grease spell created a flammable substance, the spell would say so. It doesn't say so. #DnD
Grease 1st-level conjuration Casting Time: 1 action Range: 60 feet Components: V, S, M (a bit of pork rind or butter) Duration: 1 minute Slick grease covers the ground in a 10-foot square centered on a point within range and turns it into difficult terrain for the duration. When the grease appears, each creature standing in its area must succeed on a Dexterity saving throw or fall prone. A creature that enters the area or ends its turn there must also succeed on a Dexterity saving throw or fall prone.