So it works, sort of. However, it made the spheres explode instantly after summoning, and after some changes they don't explode at all. How do I make them only explode when adjacent to an enemy?
I made some changes to your original creature and came up with something that works perfectly (I will probably use something similar).
Instead of making the creature itself burning hot, do the opposite and make it vulnerable to its own heat, then use the hot material as an ATTACK. This works.
Change the magical fire material to this:
(It will be room temperature, but will always be a gas, so when the creature dies it will evaporate instantly)
[USE_MATERIAL_TEMPLATE:GAS:CREATURE_EXTRACT_TEMPLATE]
[STATE_NAME:ALL_SOLID:frozen magical fire]
[STATE_NAME_ADJ:ALL_SOLID:frozen magical fire]
[STATE_NAME:LIQUID:condensed magical fire]
[STATE_NAME_ADJ:LIQUID:condensed magical fire]
[STATE_NAME:GAS:magical fire]
[STATE_NAME_ADJ:GAS:magical fire]
[STATE_COLOR:ALL:RED]
[BOILING_POINT:0]
[HEATDAM_POINT:10251]
[PREFIX:NONE]
Add the following material (you can adjust the temperature to make it more or less deadly)
You should add any additional syndromes to this material. SYN_CONTACT doesn't work with gases, but the explosion will create a liquid that will evaporate after a single tick, applying any syndromes on contact.
[USE_MATERIAL_TEMPLATE:EXPLOSION:STONE_TEMPLATE]
[PREFIX:NONE]
[STATE_NAME_ADJ:ALL:explosion]
[STATE_COLOR:ALL:RED]
[DISPLAY_COLOR:7:0:1]
[MELTING_POINT:0]
[BOILING_POINT:1]
[HEATDAM_POINT:0]
[EVAPORATES]
[MELTING_POINT:30000]
[BOILING_POINT:30001]
[COLDDAM_POINT:30001]
[SPEC_HEAT:1]
And then use this as the interaction:
[CAN_DO_INTERACTION:MATERIAL_EMISSION]
[CDI:ADV_NAME:Explode]
[CDI:USAGE_HINT:ATTACK]
[CDI:VERB:explode:explodes:NA]
[CDI:MATERIAL:LOCAL_CREATURE_MAT:EXPLOSION:UNDIRECTED_VAPOR]
[CDI:TARGET:C:LINE_OF_SIGHT]
[CDI:TARGET_RANGE:C:1]
[CDI:MAX_TARGET_NUMBER:C:1]
[CDI:WAIT_PERIOD:288]
The only problem is that friendly fire is still possible if used in close quarters, but that's the risk of playing with fire.
Worth noting that MAT_FIXED_TEMP is rather tricky to do clever things with, because it doesn't update evaporation and melting events normally. To make temperature attacks, it's better to use BOILING_POINT and MELTING_POINT. When using a material attack, the game will create it at the temperature closest to room temperature that it could possibly exist in that state. So a VAPOR attack (which is liquid) will be created at the MELTING_POINT if the melting point is above room temperature, and the BOILING_POINT if the boiling point is below room temperature. HEATDAM_POINT and COLDDAM_POINT seem more reliable than BOILING_POINT if you want the material to disappear once it is used.