Fortress vs. Necropolis

I suggest you study the skill tree. To ensure that fire elementals appear, you need to level up the corresponding skill in the summoning tree – this is essential. Then, fire elementals will always appear, regardless of the terrain. Regarding the phoenix: use it without fail. It won't just "distract the banshees"; it will tear through them all with dark elf magic. As for the liches, block them with stalkers; their invisibility guarantees a safe passage to the liches, or use a crystal if you get one in the guild (with high magic skill, the crystal deals tremendous damage). That's how I do it...