when you say you can the skill once do you mean per turn or something like lycanthropy (the skill is removed after the use). If it is the second case this is really overpriced.
Like Lycantrope. As for the cost, I was thinking of 2 for creature, 4 for spell, so a total of 6
Going by the card Chap showed, 2/1 still makes the spell a bit underwhelming. Having to wait a turn to use it mkaes it even weaker, so I think you can easily make this cost 3, 4 if we take into account that vanilla has no control over mulligan.
