I might have to cheat myself the unlock because a non-guaranteed level 30 zone is not something that can actually entice me, unless my AB gets it by chance.
Thalore is guaranteed to have it, and Thalore Summoners seems to be really amazing.
I'm currently running one, and after just clearing Dreadfell and winning the ambush, i noticed that i had not lost a single life since the beginning with that character !
A premiere for me, unless it's the Thalore Summoners that is that powerfull.
At first i thought the summons wouldn't be that good after having tested in the Arena, but once you get the skills going, they're -really- strong :
in combination to the Grand Arrival, the Flamespitter can truly cripple fire resistance of everything (even putting it in the negative for the monsters in a large zone) when spawning
Then you summon a big drake, that summon many other drake and deal insane fire damage
And the war hound that sounds uninteresting at first, it does a physical resistance crippling with Grand Arrival and hit very hard
And the useless turtle ? with Grand Arrival she heal everyone, you included and can take a lot of beating (and attract the attention of your enemies, that ignore then you most of the time)
Throw a golem in the middle that will daze everyone for a while with Grand Arrival.
Each 10 points of cunning allow 1 more summon at a same time, it's amazing to give a taste of overwhelming numbers to those monsters that have always used against you
And Thalore has some very good racial skills that complement things very nicely, the last Thalore racial skill summon 2 more tankers (though they don't hit hard)
The only cons is that he gain XP very slowly, i cleared everything and had to go to Dreadfell and was only level 21 or 22 (with other character i am usually higher).
The battle with the Master was very interesting, a battle of attrition mixed with minions vs minions fights with the Thalore Summoner, really the most entertaining Dreadfell last fight i had since i play ToME4.
Another bad : to optimise your summoner, you will ignore the Magic stats as you will need to put stats into Cunning/Willpower/Constituion at highest priority to improve your talents/skills and get really powerfull.
And the prodigy that gives additional powers to the summons is unfortunately requesting 50 in magic.
A combo you should play without using the auto explore, as to get the max advantage and so survival chances, you'll want to summon the Flamespitter at corridor corners to see if there's something there.
edit :
very good guide for summoners