Should I allow Prestidigitation to ignite Grease (the game allows the Grease to be flammable)?

Question

In 3.5 Prestidigitation is used mostly as a "flavor" spell. However, I noticed that in Next they added a new use for it.

You instantaneously light or snuff out a candle, a torch, or a small campfire.

PHB 267, under the uses of Prestidigitation.

Now given the flammable nature of Grease in our game, can Prestidigitation actually be used to ignite the Grease?

I'm currently DMing the game and my player pointed this out. Currently mulling to rule that it won't but I don't like shutting down ideas like this without a better reason than just "I don't like it".

Answer 1

For a strict rules-as-written interpretation, I would say it cannot unless the area of effect of the grease spell includes a candle or torch on the ground, or an extinguished campfire. Prestidigitation doesn't say anything about lighting any flammable object (like Pathfinder's spark cantrip), it specifically says a candle, a torch, or a small campfire.

But really, you're the DM. You're the one that made grease inflammable, you should decide how that changes other spell interactions with it. By a strict reading of the rules, though, prestidigitation cannot light anything except candles, torches, and campfires.

Answer 2

Sure, but keep in mind that Grease burns slowly.

If a player wants to use Grease and Prestidigitation to set up a barrier of fire before a fight, that's fine, but grease probably doesn't catch fire fast enough to be used as an attack in combat. The flames would spread slowly (I'd probably make them spread a square per round), giving NPCs a bunch of time to get out of the way, and there are tons of ways to avoid getting hurt by the fire.

One rule of thumb I tend to use in situations like this is "could the PC do this mundanely?" If they're using Grease and Prestidigitation to create an effect that they could cause using lamp oil and a torch (or some dry branches and a candle) then let them do it on a similar timescale. They get to feel cool and they're not accomplishing anything that they couldn't have done anyway.

Answer 3

It depends on how technical you want to be about the flammability of a material.

If you describe said grease spell as buttery or similar to animal fat (materials usable as casting components) than you are essentially allowing prestidigitation to light fat on fire instantaneously, meaning that effectively any biological thing, living or dead could be lit on fire by the spell. This transforms prestidigitation into a weapon rather than a special effect in this circumstance.

Unless your grease is more of an oil or effectively napalm, I would rule that produce flame would be a better choice, it already generates enough heat to deal damage, meaning that it could ignite the grease in question.

Answer 4

As the DM your primary decision should be based on how much fun does this idea add to the game.

If it becomes an optimal strategy that the players will use all the time it's probably not a good idea to include. However if it happens rarely and in interesting situations then it might be worth including. Maybe having a house ruled roll for success on it would balance things.