Good ideas! Some problems: Kraken is already a spell. The Krokomummy is a treasure card, but it would be cool if it were actually a spell you could learn. I think that a genie is already incorporated into one of the level 58 spells... fire? not sure, but it looks like a genie.
Yeti= Bigfoot= Forest Lord Cthulhu is a sci-fi entity, not a mythical creature. Most kids wouldn't get the reference. Basilisk- aren't there already enough snake spells? Hippogriff- just no, use a gryphon not the outcome of when one loves its food too much (look it up) Genie= Efreet Kraken= Kraken duh Naga= Gorgan= Medusa