Dungeons and Dragons: Mithrondil's Spell Book, Page 6

Mithrondil found himself engaged in war. His kingdom was under attack and, at first, he didn't know who was behind it. It turned out to be the work of a demon. The war was terribly frustrating, in the fact that it came in waves. Every time the enemy was driven back there would be a few days of rest and then an even stronger force would approach. Eventually, even the demon himself would appear on the battlefield. Mithrondil went out to meet him face to face and fought with the demon, who would stand a while and then vanish. It seemed that there would be no end to this war, because he couldn't defeat this cagey demon. So, he consulted all of the sages in his kingdom and one uncovered some information about the demon; who he was and where he had come from. Armed with this knowledge, the next time the demon appeared, Mithrondil and some of his companions followed the demon home when he sought to escape. They did, of course, manage to slay the demon and they returned from his fiery realm, the demon's treasure hoard in tow.

It was quite a challenge, just to survive in such a place, let alone overcome such an opponent, and it gave Mithrondil the idea for this spell. The hellfire seemed to burn hotter than the fires of the Prime Material Plane, that is, the world where people live. It had taken all of the protective spells the party could muster just to reduce the pain of walking and breathing to a level that could be endured for the time they were there. Mithrondil set out to mimic this heat in a spell of his own devising; Fires of Hell.

This is, in essence, a double strength Fireball spell. The range is the same as for a normal Fireball, but it burns twice as hot and the area of effect is double, so its blast creates a sphere of 3" radius (30 feet indoors or 30 yards in the field), instead of diameter. Damage dice for this spell are D12, instead of D6, the number of dice rolled being based on the caster's experience level, up to 10D12, and victims may save for half damage. At the low end, this can still be 10 points of damage, or save for only 5 points, but at the upper end there will be 120 points of damage taken by those who fail to save. It is not the most deadly spell in his arsenal, but it was adequate in most cases where it has been used.

It is sixth level of spell use and the material component is extremely rare. The caster must hurl a gem that he has personally stolen from a demon's hoard as he speaks the incantation. The gem transforms into a ball of fire and streaks towards the target, exploding when it reaches the caster's designated range. Since Mithrondil has only a limited number of these gems, he is reluctant to use the spell unless the need is great. This is an excellent example of one of the ways for a Dungeon Master to impose limiting factors on spells created by his players. My DM insisted on this material component, knowing that I had only a limited supply of gems from the demon hoard. If I used them all up then he wouldn't have this spell in his campaign anymore, unless I wated to track down and defeat another demon.

Next up, how to use a fireball without singeing the toes of your halfling friend.