My favourite version of Kroak was 5th ed (not just because of the artwork), he was...a little hard to fight against. Beyond that, my next favourite version was 6th, he was the ultimate glass canon, in 2000pt lists he was hard to use properly, but devastating if done correctly. He could even hold up (and beat Archaon in CC), despite not having any attacks (higher unit strength, auto strength 5 hits against his daemon steed, makes Archaon's sword simply a basic hand weapon, meaning he needs 5's to wound Kroak).
Just looked over these rules... what a beast! This is the first Kroak I was introduced to when joining Lizardmen. It was fun having access to the most expensive character in the game. Powerful... but risky!