Tactics for complex battles.

It depends, and it depends a lot :) Roughly speaking (as stated in the manual), 1 druid casts Lightning as a hero with a magic power of 1, 3 druids with a magic power of 2, 10 druids with a magic power of 5, and so on. This applies to all spellcasting creatures. In addition, the LEVEL of development of the corresponding magic, assigned separately for each creature, is also taken into account. For example, an archmage casts such a devastating strike as if he were an expert in light magic (+12 to offense), while the mistress of shadows casts Weakness at a basic level (half the stack). At some point, the effectiveness of damaging spells drops sharply (when there are approximately 50 creatures). Then, it is better for the same archmages to switch to ranged attacks or split into stacks. P.S. This issue is discussed in detail in the manual.