Fenrir: Heavenward Howl (Lv. 96)
Grants the effect of HP Drain or MP Drain to party members within area of effect.
Diabolos: Pavor Nocturnus (Lv. 98)
Lures an enemy into an eternal nightmare.
So, fenrir's ability if it isn't at least drain samba 3 is useless. And since it would fight with Haste Samba, it's not very useful in any circumstances.
I can't help but notice the "eternal" word there. Undispellable, unending debuff? That would actually be awesome and overpowered. I'm guessing it's actually a very potent dark based sleep. I've always thought that Diabolos was the premier support avatar. Giving him more sleep makes sense.
So, I'm not amazingly impressed with the spell upgrades coming. My remaining hopes for summoner are new ja's, and new avatars from WotG. So depressing, summoner has the richest story in the game, and the greatest interaction with the cities in the game. And here we are.