What level was the mission set at?
I know you can solo an AV if you are a scrapper with mish set to heroic. (granted then they are EB's)
Did this at level 46 set on invincible with.
1.Stone/mace tank
2.katana/regen scrapper
3.kinetics/radiation defender<----me
It required spamming transfusion to lower the regen rate and the tank was smart enough to pull infernal back to the doorway withought aggroing the portal.
3 man avs are definitly doable but I think they require decent builds and a team that is used to working together to pull off.
Taking It On the Chin I-16 Tanker Guide
Repeat Offenders
Tried this with a fire/kin and 3 */rgn scrappers. Even spamming everything I had, the scrappers and my imps went down quickly. He's a tough one because he hits hard. We made a dent in him, and had him away from the portal so nothing spawned there, but a string of two missed transfusions and a missed transference was all he needed to wipe out the melee folks. Sometimes, even with 2 green Acc SOs and tactics, you just get a bad string of numbers.
[ QUOTE ]
I know you can solo an AV if you are a scrapper with mish set to heroic. (granted then they are EB's)
[/ QUOTE ]
Well then, you aren't really soloing an AV if he is an EB, are you? 
RagManX
"if the market were religion Fulmens would be Moses and you'd be L. Ron Hubbard. " --Nethergoat to eryq2
The economy is not broken. The players are
You can duo him, actually.
Tank stands 10-20 feet away and taunts. He'll fire Flares over and over at the taunter, which for most tanks and scrappers is a joke.
Second team member, preferably someone with -Regen, kills the AV. It's slow, but he'll go down. My Fire/Rad troller killed him in about 10 minutes this way.
I duoed him with a lvl50 fire/kin/fire and a lvl 24 Illusion/rad that I sidekicked on unyeilding (so he was an AV, not an EB). The siphons and FS kept his damage in check, and AM (+SB on AM caster)+ Hasten + Siphon speed got the imps back often enough since he can one shot all 3 of them with his AoE.
PA came in handy also to keep him occupied at a few crucial times. We both got in the red a few times, and I was full out of inspirations by the end, but we got him. I have the fire Epic so Fire Shield did cut out a lot of his damage too (I managed to keep all aggro away from the Ill/rad)
No temp powers, shivans or nukes. The inspirations were whatever I had in my tray at the time, no hand-picked (we originally started the mission to try and level him up to 25 for a TF, then once we got to Infernal we said "why not?")
The same duo took a Malaise down, but I think we had to try 3 times before we got him: no resitance to Psi and he has holds.
Infernal can be rough, since he "can" hit so hard. I think he splatted me once or twice last time I took him down. But that time I had a full team, so I didn't bother with Inspirations, and he wasn't as defensively debuffed as he would have been if we'd had a smaller team. Smaller team and I'd have used different tactics, more inspirations, brought along my DDD instead of my scrapper, etc.
You "can" solo "select" +0 AV's - with shivans and nukes, it's been done.
I have little difficutly Duoing most +1 AV's, no shivans, no nukes. I'm not sure if I ever Duo'd Infernal, but it should be possible, at worst, add inspirations, Shivans, and Nukes.
Almost all +2 Av's tend to stalemate with just two. However, add a third man, or Shivan's and Nukes, then things will go smoothly enough.
The last +2 (Level 52, we had also just duoed three or four +0 and +1) AV I duoed, was my 50 DDD and a 48 scrapper, and we stale mated. The Scrapper at -4 couldn't do enough damage while the -regen spiked from hasten TG and HT. We stalemated at about 40% damage, then Hasten expired and the AV managed to creep back up to 20% before Hasten recharged. We might have eventually worn him down, but it would have been forever. Add a 50 scrapper, splat, dead AV in less than 2 minutes. We were stalemated before, all we needed was something to push us over the edge.
AV's you really need to watchout for Small team are the ones with Auto-Hit effects, Aura's, and PBAoE heavy melee. Inferno (spelling) the Axe Hero (Not Infernal the demon AV) was one of the worst ones I ever accidentally got too close to. We learned our painful lesson: AoE, splat, wipe. Came back and made sure we overloaded defense (inspirations) and overloaded debuffs before we closed in the second time, then kicked him where it hurt.
Can everyone do that, no. -Regen and Debuffs are essential, and given AV resists, massive over debufffing is a really good thing.
Given the resists, the regen rates, combined with average player skill, I'm also not surprised when a "random" 8 man team can't kill an AV, especially the +2 type of AV. I can think of many team combinations that would fail, more that would fail than would succeed. With that in mind, that the fact most pickup teams just add warm bodies till they can't add warm bodies any more, no, I'm not surprised when a "random" team fails.
I've had the pleasure (or agony, depending) of facing Infernal in combat many times. Without exception, the most trouble free time was a team of four: Myself (Lvl 45 INV/SS Tanker), and three SG mates (Lvl 40 INV/SS Tanker, Lvl 50 MA/SR Scrapper, and a Lvl 50 EMP/RAD Defender). Set on Invincible, I was worried about this fight. My Tanker is a Heavy Assault Scrapper and the other is a pure Tauntbot. We split the room into two sections, with the Scrapper and Defender taking Infernal, the Tauntbot taking all (and I do mean all) the summoned minions, and myself moving between each group. We have all teamed together many times and with some practiced coordination and tactics, the fight was over fairly quickly.
Overall, I'd agree with most of the responders above...the idea team size for AV's seems to be 4-6. Oddly enough, team composition never seems to matter nearly as much as solid tactics and cooperation.
the other day me and 2 other people killed infernal (the praetorian)
this is how we did it
the team:scrapper:claws/dark armor, controller: fire/empathy, controller: illusion/empathy
how: the controllers buffed the scrapper with 2 ras of both kind gave him 2 forts 2 clear minds and 2 ABs
the illusion controller mezzed and fought the portal while the fire controller mezzed the portal and healed the scrapper