-1 to festive and (tentatively) electroslog.
Consider this:
1)Slog is somewhat fire-inclinated.
2)Making him electric would probably remove frizz.
On the other hand, Goombess could perfectly get a magic spell to make her more powerful, unless we plan on keeping her in the Underside.
Frizz is a pretty standard Dragon Quest spell... so I doubt he'd lose it... plus the Dark Cathedral in SMT usually lets you pass skills on to the result.
Frizz is the weakest single target fire spell. (Fun fact: It was called Hurt back when the series was called Dragon Warrior and eventually got changed to Blaze. Ultimately, they changed the name again when Square and Enix merged.)
Though oddly in the first Dragon Quest Monster game, Slimes learned Sizz (called Fireball back then) which is the weakest multitarget fire spell.
Hopefully that means he won't be learning the second Slime spell from DQM. Though it may be useful in this game though.
The third spell a Slime learns in that game was the best spell in the game (Slimes were weak, but if you could get one to learn that spell you'd be able to breed it to a monster that could take full advantage of the spell early on in the game. Interestingly enough you wouldn't know this your first time through the game and the mechanics were simple enough to figure out but complicated enough to trick you into thinking your first Slime couldn't learn it due to the level cap. But on a second play through an experienced player would know how to get the spell from their first Slime and makes the game significantly easier.)
Ah... I've been a DW/DQ fan for a long time...