An enemy that cannot move or act is an enemy that cannot hurt you. Slowing and stunning are some of the most powerful abilities available in most games. A clay golem may be easily slain in normal difficulty by any boss, but in hell difficulty his hit points go into the hundreds to thousands (even at skill level 1!) This leads to incredible damage mitigation, as you will rarely be even targeted by an enemy due to your mobs. You can get anywhere in the range from 10 to 30 allies depending on your build. Summoners put up a lot of bodies with a lot of health.My experience fighting all of hell as a summoner in single-player, bosses included, was mostly a cakewalk. I would argue that summoning necromancers are the easiest character type to play through hell difficulty with.
