D&D 5E FrostFire / FireFrost spell - homebrew - thoughts?

[Mark1733]

I have a 3rd level arctic adventure and would like the enemy winter warlock to have the following spell. Since the party is expected to have fire-based damage dealing spells, and the warlock's minions will be in part cold-immune (i.e., fire vulnerable) creatures, I was thinking he could have a spell to do one of the following effects:
1) Rather than counterspell, it could be cast as a reaction to convert the "hot" fire effect of a spell or ability to "cold" fire, causing cold damage. I would expect to have to meet/beat the spellcasters DC.
2) Or create a gentle flickering blue fire in a 10-ft radius that negates fire vulnerability to cold-based creatures standing within it and causes 1d6 cold damage to any normal (2d6 to cold-vulnerable) creatures. Dex save to avoid the flames. Any combustible surfaces will "catch fire" and spread accordingly but burn cold.

It would be instantaneous if 1) and a concentration spell if 2).

Thoughts? too strong? too weak? too silly? there is already something out there just like it?

Thanks in advance for your ideas.

Obi

 

[Eltab]

The 3e supplement Frostburn has some special cold-based spells.

I like idea (2) but would tie it into an amulet or similar rather than a cast-able spell.

 

[Mark1733]

I updated the full description as a spell as follows. I am looking for feedback. I have set it up as:
2nd level evocation spell
1 action
60-ft range
20-ft cube* (can spread)
duration of 1 minute; requires concentration

You reach out your hand and splay your fingers, rhythmically undulating them across the area of effect. A blue frost forms over all surfaces within a 20' cube, light blue flickering flames alight, and cold emanates throughout the volume. All normal fire in the area is immediately converted to this blue fire and starts radiating cold. Combustible materials will ignite like normal fire and spread similarly into a larger area 5 feet per round (if such materials exist there) , but will radiate cold instead. Additionally, all surface water in the area freezes, making such surfaces icy (i.e., difficult terrain; failed dex check results in falling prone). The area of effect can get larger as a result. However, no materials are consumed in the combustion. Any magical fire (e.g., flaming sphere, scorching ray, etc.) originating from a spell of a level equal to or lower than that of the spell cast will instantly be converted to "frostfire" when it enters the area of effect and deliver cold damage instead of fire damage. Additionally, any creatures vulnerable to fire can ignore the vulnerability as long as some part of them is within the volume. So, for example, if cast at 2nd level, the fire from a fireball (lvl 3 spell) will not be converted to cold damage, but any creatures vulnerable to fire will not take double damage if hit by the fireball. When the duration ends (or if concentration is broken), all fire is immediately extinguished. At higher levels, the spell can effect fire from higher level spells (example: cast as a 3rd level spell, the fire damage from fireball can be converted to cold damage). The level at which it can be upcast maxes out a 5th.

 

[Mark1733]

The 3e supplement Frostburn has some special cold-based spells.

I like idea (2) but would tie it into an amulet or similar rather than a cast-able spell.

I like your idea of using an amulet. It becomes a treasure for the group for future use, assuming they destroy the monster using it.