As for KANTUCHDIS, I think stackable would be unfair unless it couldn't give more than a 30%
As for WONAFYT, How about making it summon your level or higher starting with your level then check one above, then two above, etc. A possible overhaul for WONAFYT could be it temporarily increases the level and stats of a monster until you regenerate or attack another monster.
We made an expansion and it is awesome. Really, you should check it out, especially if you're looking for some extra challenge.
Download over at ddmod.weebly.com!