Dark Thrain (Thrain)

Thrain (Dark Grim Reaper) is a good crowd control monster in Summoners War.

He is very useful in ToA since he puts dots AoE without inflicting damage, so he comes in hand when used against floors with monsters that counterattack like Wind Monkey King or Light Yeti or also monsters that buff attack bar like Dark Dragon Knight.

Moreover, his third skill is AoE with five hits that hits random targets (he can strike multiple hits on a single target), and also he stuns for 1 turn the enemies under continous damage effect. 

With this skillset he is best runed Violent, since you can use the second skill, Violent proc and then use the third skill to stun the enemies under continous damage effect.

Keep in mind also that his first skill, if he kills, he gains another turn.

Thrain in ToA is very good also if he is alongside with AoE dotters like Baretta, Zaiross, Water Homunculus etc.

Remember also that Thrain is very squishy and on higher floors of ToA (especially the Hard mode), he wuold die probably with just one hit, depending on his stats of course. For that reason is better to pair him with someone like Spectra that can slow down enemies and keep their attack bar low!

Thrain rune Build

Violent Build: Violent/Focus or Violent/Accuracy - SPD / %HP / %HP or SPD / %Crit Dmg / % ATK with speed accuracy and attack substats.