I had this issue today Where one of my players cast Chill touch on a troll they had encountered to stop it gaining it's regeneration ability. The wording in the spell reads as "On a Hit, the target takes 1d8 necrotic damage, and it can't regain hit points until the start of your next turn."
But in the 5e Monster manual the entry on troll regeneration reads " Only Fire and acid can stop a troll's ability to regen."
Could someone please give me an exact ruling on this please?
The troll's ability should read, "only fire and acid (or abilities which specifically prevent the regaining of hit points)".
Someone could give you an "exact ruling," but it wouldn't necessarily be any better than your ruling. You've got two conflicting specific rules.
That said, the regeneration property says "Regeneration. The troll regains 10 hit points at the start of its turn. If the troll takes acid or fire damage, this trait doesn't function at the start of the troll's next turn." That's a bit different from saying "only acid and fire can arrest the regenerative properties of the troll's flesh." That latter quote comes from the more flavorful description, while the former quote comes from the actual mechanical description of how the power works. Given that, I would think that chil touch would indeed stop the troll from gaining hp, since with the two mechanical rules side-by-side, chill touch seems to provide a more specific exception to regeneration. Moreover, it seems *to me* like the 'mechanism' by which chill touch prevents other creatures from healing would apply in the situation of the troll's regeneration as well. But this is an area where you, as DM, should feel fully empowered to decide either way.
One could interpret that if a Troll doesn't regain the 10 hp, it didn't "regenerate," and thus dies. In this scenario, the chill touch spell would kill a Troll.
Another interpretation is that chill touch can temporarily incapacitate a Troll, because it's at 0 hp and cannot regain hp. However, only fire or acid damage will "kill" a troll. The spellcaster could keep hitting the troll with chill touch until another character attacks it with a lit torch (improvised melee weapon attack with advantage, automatic critical, 1 fire damage).
A power word: kill spell could kill a Troll outright, as an alternative example.
So there is currently no difinitive ruling on this, it is just a judgment call on my part as the DM?
Jimjams wrote:
Like how feats over-ride normal rules in some situations, powers that specifically target a type of function should over-ride anything that someone else can do. Especially in the case when the very thing it's over-riding is stated in the description of the attack.
If trolls can't be killed via frost; then you can at the very least keep it from attacking other people.
I'd say that chill touch does work to stop a troll's regeneration. A strict reading of the troll's Regeneration trait and the spell description would seem to indicate that, but in any case, it doesn't hurt to side with the player in this situation even if the rules weren't as clear as they are.
Specific beats general. The regeration is a general rule regarding damage while chill touch is a specific property of the cantrip. I would rule the cantrip prevents regeneration on the following round.
Tsulia wrote:
Yes - it would stop the regeneration, and kudos on your player for using it - creative and effective! 
Generally, only Fire and Acid stop a troll's regeneration. Specifically, Chill Touch stops all.
(though, you could also argue that Fire+Acid is Specific to the General regeneration rule, so you have a "Specific Vs. Specific" clash, in which case a DM decides, and either way is plausible. Though I'd be okay with Chill Touch working, myself)
Timborama wrote:
I think we can expect a certain amount of utility for each cantrip or spell. Not being able to affect a troll's regeneration cuts deeply into that utility, so I would rule chill touch would negate the regeneration.
One of the main draws of Chill Touch over other attack cantrips, is the secondary effect. I think it would be unfair to append the disclaimer to chill touch "but it only works sometimes." Fire Bolts has the same effect on the troll regeneration, after all, so I would have no issue at all with allowing chill touch to do what it does.
I would rule that the Regeneration triggers, because there was no fire or acid damage, but no hit points are regained, because Chill Touch specifically prevents that.
Therefore, Chill Touch can keep a troll below zero hp, but can't kill it.
jonathonhawke wrote:
jonathonhawke wrote:
I like the interpretation that Regeneration can be functioning, but the creature regenerating still not regain hit points - it meshes well with the description of hit points in general being many more factors that just the physical meat of a creature, and with the truth that things which cause physical harm to the body (pin prick, paper cut, slap to the face, etc.) do not necessarily cause a loss of hit points.
It's regeneration is still working and keeping it alive, but it isn't working to such a degree that it constitutes a change in hit points.
paulstrait wrote: