Want more immersion in Skyrim? Want to see a village of farmers who are preparing to fight a troll ? Or be surrounded by 4 bandits, then be saved by a furious mammoths? This mod adds the possibility of encountering Bandits, Vampires, Thalmor, Necromancer, Atronach, Werewolf, Mammuth, Dragonpriest, Dremora, Boss and Giant Monsters and other, with a small chance of them meet together or 2 factions in one time: this creating faction battles and make the game more difficult.
Be careful, it seems to raise the general combat difficulty of lower enemies as well but it makes the vanilla (rather borish) Skyrim adventuring much more fun/gratifying (imo).
http://www.skyrimnexus.com/downloads/file.php?id=6176
