I think he is a viable choice in 2k games, maybe better on 2250...
But the list will be sort of Star Dragon... Put Kroak on a 11 Temple Guard unit (they are unbreakble so they don´t need to be full), this way you can save some points, put 2 Engine of Gods, one on each side of the TG+Kroak Unit... A unit of 3 sallies, and about 4 units of skink skirmishers, this to outflank the enemy... Use the flank denied tatic and MARCH over the enemy.... You can think that a few enemys could stand against de 1D6 from each engine of gods plus 2, 3 or even 4 d6 of damage from kroak magic, in every unit near!!! In one or in two rounds the enemy shall fall...
Furthermore, i believe thas this list/tatica will give the game only one result, massacre, this list will massacre the opponent or the opponets will massacre you... no normal victories or draws...
It´s funny anyway !!!