Which monster do you like the most in Heroes 5 (level 6)?

Yeah... I guess you're right about the Knights :). But there are no invincible strategies – there are only invincible players. As an example, I can imagine a Warlock overcoming anti-magic – we take control of the Seraphs, and after the Knight (under anti-magic) has killed 1-2 units, we bombard him with Divine Retribution :). Or, there's a simpler, but at the same time worse, longer, and more tedious option – gathering undead from neutral creatures, which mostly depends on luck (whether there's enough energy for the most needed creatures or whether creatures with the Messenger of Death ability join). But otherwise, it's almost uncounterable...
P.S. sorry for the off-topic.