I don't have a Critical success table for spells, but here is a short list of potential fun fumble options.
I made them up with input from my players.
1. Blanche! - Caster skin, hair and eyes are drained alabaster white. Effect lasts until a difficult (-20) resilience roll is made. This roll can be attempted once per day. Once made, the Caster will return to normal in d6 days. Halve the Casters effective CHA score, and influence skill for the duration of the blanching.
2. Mixup, Self! - Spell is cast on user (if harmful) or random nearby foe (if beneficial). If item based, on nearby random item.
3. Mixup, Other! - Spell is cast on nearby companion (if harmful) or random nearby foe (if beneficial). If item based, on nearby random item.
4. Stunned!- Spell failure stuns the mind of the caster, creating the same effects as combat stunning (loss of 1d3 CA, but can still parry or evade).
5. Bamph! - Spell creates a puff of smoke, a loud noise, a bright flash, and awful odor, etc. No other effect (although, if the point was to remain silent, this could have another effect...)
6. Illusory effect! - The spell seems to work, but the effect is an illusion- GM should try to convince everyone that the spell did, in fact work.
7. What was that? - Spell fails and caster temporarily forgets the spell. Roll the spell skill once per week beginning the next day to remember the spell.
8. He's not with me! - Caster accidentally summons an angry elemental- Roll randomly for type and size (1=Gnome, 2=Salamander, 3=Sylph, 4=Undine) . The Elemental can be dispelled or bound. It will not just leave though. It is permanent.
9. He's not with me either! - Caster accidentally tears the veil between realities and allows a Spirit to enter. Roll randomly for type (1=Bane Spirit, 2=Sickness spirit, 3=Ancestor Spirit, 4=Nature Spirit, 5=Guardian Spirit, 6=Curse Spirit), strength (Intensity= d6-1 x 6 with lowest intensity being 1) , and temperament (1=Friendly, 2=Friendly but with seeks payment, 3=Neutral, 4=Unfriendly, 5=Hostile, 6=Very Hostile). Spirits can be bound. Hostile and very hostile will attack caster immediately. GM's choice of how to deal with the others.
10. Loss of Confidence! - Spell fails and all subsequent spell attempts are at -10%. A persistence roll can be made once per hour to shake the demoralizing effect.
11. Loss of power! - lose twice the MP you spent.
12. Costly magic! - lose three times the MP spent on the spell
13. Wild Magic! - Spell effect get warped (Attack spells attack multiple friends, fly sends things around you to the air, Telepathy mean you are broadcasting everything, magnitude of spell increases dramatically, mix and match any of the above, be creative-GM's choice).
14. Tiring Magic! - You gain a level of fatigue per Magic point spent
15. Flare out! - Your current MP total is cut in half and you gain 1 level of fatigue
16. Blow out! - Your current MP total is decreased by 3/4ths and you gain 2 levels of fatigue.
17. Gassed and Passed Out! - Lose all of your MP's and pass out. Regain consciousness and MP's as normal. Dangerous around the wrong group of friends.
18. Backlash! - Spell magnitude is transferred directly into damage points. All of the damage is taken by a random hit location. Armor and Magical armor will not protect against this damage (it is essentially internal, and "inside" your defenses).
19. Blow up! - The mystic energies being manipulated go wrong. Horribly wrong. An explosion occurs doing 1d6 damage to the arm used to cast the spell. If a 6 is rolled, the roll is made again to a random hit location (this can include the same arm). Armor does not protect against this damage, but magical armor will- unless the armoring spells magnitude is overcome by the total damage value, in which case the armoring spell is dismissed.
20. Narrow Escape! - The spell has no other ill effect outside of the normal loss of MP.
