Gameplay tactics on the S map.

Hero activity, selecting heroes based on starting troops and STARTING MAGIC, defending castles with heroes possessing the "war machine" skill, the "scouting" skill, and, most importantly, competent turn management (without this, it's absolutely impossible to succeed on such maps).

As for scouting, I'm not sure..., but artillery is definitely a must-have for a guardian hero – that's a fact. The main hero should generally have starting magic that deals damage, for example, archery.

I've also tried playing without choosing any specific faction at the beginning – they gave me Necropolis, and I won against 8 AI opponents solely due to the vampires, although they weren't even upgraded..., but retaliation is also a powerful ability.