I don't think it's even that. I started asking about it in guild after a botched Moroes attempt with 1 priest. Our strategy consisted of 1 shakle, 2 pally fears, and 2 kills. With the shakle, fear, and moroes up the fiend went straight for the shakle, the priest reshakled multiple times and every time it was instantly broken by the fiend. The add was also currently shakled as the fiend was cast, with Moroes as the current target after just coming back from a vanish.

Definitely not proximity. For last night's Wizard of Oz event, I targetted Strawman, ran inside his model, and dropped Searing Totem. It started attacking Strawman, but when I went back to Dorothy, the totem went back to Dorothy. However, I am sure it's also not the closest target to you either, because I've had a Searing Totem attack Julianne while I was on Romulo (don't ask why I was on Romulo).

This could be the most important question ever asked.

I remember being in scholomance with a rogue useing the full Eshkander set, and every time it proc'ed we wiped. The stupid thing had a habit of pulling the rest of the mobs in the room. One wipe from an additional summoner pack in the summoing chamber. Again a wipe later on clearing out the room prior to the viewing room. It seems that pet had the pet on agressive scripting when it came into play.

If I was a programer, i would make it cycle. Pet spawns acts right once, then go after croud controll the next time. Then I would read threads like this and laugh.

Shadowfiend usually attacks your current target, the problems start when your target does a special ability (like garrote) or is being crowd control as well. He will never attack a sheep or a shackle if there are any other possibilities but once there aren't it's basically fucked up. Yesterday in shadow labyrinth heroic I used my shadowfiend on the zealot packs right after a fear, the shadowfiend ran to an unpulled pack, pulled it and ran straight back to me.

At least that's my experience with shadowfiend :p

Hm, that's pretty odd. I'll try to replicate your results on our next raid.

I've been using a grimoire skeleton forever, and it seems to follow normal mob rules. I've never really paid close attention to what it does, though

Ancient Cornerstone Grimoire's skeleton - at least for the year or so I was fond of it (my first epic lol) - NEVER EVER EVER attacked a damn thing until I got hit. No matter what I was targetting or not. It could of course be different now, but I remember many a time on Onyxia and Nefarian, and many MC bosses, when I would have to wait to be feared, cursed, physically struck, etc., before that damn skeleton would even move.

Well, I guess for those of you who have never used ACG (or Benevolent Mr. Pinchy - thanks for the info), the wording on the ACG is very distinct: "Skeleton PROTECTS you for 1 min.". It doesn't say anything about attacking the enemy; it is clearly a defensive pet.

This is in stark contrast to other Use: ability pets, like the Mechanical Yeti from Everlook - it clearly says it will "fight for you" for 10 min. and there are several other examples. Shadowfiend would fall under this category.

Conclusion: You can't really compare the ACG Skeleton to the other Pets/Totems in this discussion - because it clearly is a defensive pet with different AI than Fiend, etc.

oh, good point. I never even thought about there being that kind of distinction between uncontrolled pets

This is not quite what happens. Shackle generates some static amount of threat (very low, though), but it does not freeze the threat table. You can generate threat on a shackled mob via Demoralizing Shout or Sunder Armor (of course assuming you don't break the shackle by doing damage).

However, shackled mobs completely ignore threat from healing or buffs. In fact, healing threat is split evenly between all non-CCed mobs. If you have five mobs, out of which two are CCed, the remaining three will each register 1/3 of your healing threat (not 1/5), assuming all of them have the target of your heals on their threat list (if they don't, then healing threat is split only between those mobs that have the target of your heals on their threat list).

Had our priests test this last night. We had a shadow priest so I had only him use his shadow fiend on Moroes and it did go right to Moroes and stay on him. For Curator I told every priest to cast SW:P and then hit their fiend as soon as his evocate starts. Usually we have fiends go after the last flare, but this time all 3 priests' fiends went straight to the Curator. Only one test I know, but I think this is the rule to follow for shadow fiend.