The story of Solmyr and the Efreet is the special scenario in Might & Magic: Heroes VII, available only in collector's, complete & deluxe editions.
Overview[]
Solmyr starts with one level 1 Academy and a special ability to cast an extra powerful Chain lightning spell. There is a Stronghold forces to the east and a Necropolis town to the north. The player doesn't need anything from these cities but the magic guilds and income. The problem is that they will obstruct player's progress until they are conquered. Concentrate on one and let the other go (within reason). Once the two cities are taken, there are three altar/seal combinations the player must bypass to reach the efreet.
Early on, the player will want to use Solmyr's Chain lightning almost every combat. Use stacks of gargoyles to absorb the lightning if it reflects back on the player's forces (gargoyles are immune). Later, when the enemy stacks become huge, Implosion will be the best bet. Once the player can cast two spells each round (as long as the first is a Prime Magic spell), Implosion followed by a holding spell like Blizzard is most effective. Don't forget the player can summon Elementals adjacent to shooters to gain more time.
If the player can start buying up the neutral creatures early, they make an excellent second army. Shantiri titans, shantiri golems, fire elementals, water elementals and dark elementals make a powerful force once the player has a few weeks' worth.
As long as the player has been careful not to take too many casualties along the way, an army of Academy creatures should win the last battle easily, with Solmyr's excellent magic.