I would raise basilisks in the "ranking" of level 4 creatures – they are a serious opponent; you can rate them 4 out of 5. Good defense, acceptable speed, attack, and survivability + an excellent feature with petrification (it works often). A unit taken out of action at the right time is sometimes more valuable than any damage! Vampires are stronger, of course, but I would compare griffins and ogres to basilisks – they all have their own features, and they partially offset each other...
Dragonflies can also be annoying with their speed and ability to remove spells.