D&D 5E Would you allow this combo?

[Harzel]

I would allow it because, as others have said, it used up resources and it's cool.

Flame arrow: When a target is hit by a ranged weapon attack using a piece of ammunition drawn from the quiver, the target takes an extra 1d6 fire damage.

When the arrow transforms into a lightning bolt, the original piece of ammunition drawn from the quiver never hits the target. I wouldn't allow it to stack.

I had a similar thought - that the transformation of the arrow into a lightening bolt would cause it to lose properties (even magical ones) that it had as an arrow. However, the part of the spell description quoted (a ranged weapon attack using a piece of ammunition drawn from the quiver) would actually make me inclined to allow it, because the attack definitely did use a piece of ammunition drawn from the quiver. It is the next part of the spell description that would make me hesitate: "The spell’s magic ends onthe piece of ammunition when it hits or misses." That indicates that the magic is carried by the ammo itself rather than being associated in a more general way with the attack. That said, I'd still allow it.

I also wouldn't allow fire and cold to add on the same weapon attack. Rather they would subtract.

Would this extend to, say, Cone of Cold and Fireball cast on the same area in the same round?

That's how I would call it, but I have a bug for realism.

I sympathize to some extent - you want the world to operate in a consistent and believable fashion - but I think it's possible to find a narration that makes it work. The icy mote at the tip of the lightening bolt plunges into the creature, freezing its core while electricity courses through its body and flames ravage its exterior.

Next question: If I coat the tip of the arrow with poison, does that work, too?

 

[Coroc]

I would allow it per the rules, but I'd pull the player aside and have a little talk about how crappy Lightning Arrow is and that he should never cast it

Actually though, I wouldn't say RAW was clear. Lightning Arrow says

A DM would be in their rights to rule that the flame arrow spell and cold bow effect contribute to the arrow's "normal" damage and would thus get replaced. In any case, you wouldn't deal any piercing damage.

So there we go, thanks for the spell description, in this case lightning and cold ok, flame arrow and cold ok but not lightning, fire and cold. It is like two competing spells on a single normal item. It is like casting light and darkness at the same character.

Lightning arrow does want to make a lightning bolt out of that arrow, flame arrow wants to make a burning normal arrow out of it. Both spells are magic effects as is the cold from the bow which is always on, since there is no mechanic behind it detailing how the cold damage is transmitted it always works.

But the lightning arrow requires an arrow, it does not care if this arrow is on fire or whatever it just transforms it into a lightning bolt. The flamearrow spell requires an arrow as spell target so it will not work on an lightning bolt.

Fazit: In this situation it will be always lightning + cold, either because the burning arrow is transformed into a lightning bolt or because the flamearrow spell finds no usable target.

 

[GMMichael]

I'm curious why one wouldn't allow it?

Because heat negates cold? And vice versa?

If an arrow still has enough structural integrity after having been charged with three different elemental powers (it's just a stick of wood, people), I guess I'd let the electricity damage stick.

 

[kalil]

Yes. If the players think this is cool and want to do it I see absolutely no reason to rule against it. "Realism" arguments applied to magical spells in a fantasy rpg are fundamentally silly.