You will not evade me, $name

[Tallenn]

Here's the way I remember it. In Kunark, it was mobs over level 50 that could summon. That changed over the years, but right at first, that was the toggle: 50 and below: no summon, 51+: summon. Nowadays, level doesn't really have much to do with whether or not a mob summons- LOTS of mobs over 50 from POP on that didn't summon (had to- as players kept getting higher levels). I think that after a certain point, the devs just started deciding on summon or no based on how they felt was best for game balance on a case by case basis. That may have even started in Velious, but I can't say for sure. For Kunark though, it was completely level based between 50 and 51.

As to how it works, from what I remember, it was a special ability, just like lots of other special abilities. In other words, it has a recast timer. Once used, it can't be used again until the recast timer is up. It seemed to be like 4 or 5 combat rounds for most mobs, but it could vary from mob to mob.

Who the mob chooses to summon I always thought was simple. If the person on the top of the hate list wasn't in combat range, it would summon them. So, it wouldn't necessarily summon right away once the recast timer was up- not until someone not already in melee range managed to get it's attention. You only have to be on top of the hate list for an instant too, because I remember being summoned many times, and not even getting attacked. In other words, the mob had already switched to someone else from the time it summoned me to the time it's next swing came up.