This idea has probably been brought up in the past, but I can't remember in what sort of incarnation.
I thought this one out for a while to avoid possible forms of abuse, such as just spamming the spell to lock out an opponent, while keeping it tactically viable.
I was thinking a mentor level spell, sorcerors and necromancers are the best fit for this I believe, possibly priests.
The spell can't be cast until your
opponent starts casting a spell. The counterspell itself would have a very short casting time, something similar to magic missile or cure/cause light. You basically have to do exactly what the spell name suggests, catch your opponent in the middle of a spell cast, and try to counter it.
Now, I've also thought of some drawbacks for the spell, so that it's not just spammed on a target. First the spell should have a fairly moderate mana cost, something along the lines of dispel magic mana cost, which is around 4-7% for a human caster at GM.
Secondly, and this is the big drawback, and in my mind what makes the spell balanced. If the caster successfully counters an opponents spell, the
caster of the counterspell is charged the mana cost of the spell being countered, plus the mana cost for casting the spell as if the counter failed. So if a mage counterspells a priest who was in the middle of casting holy word, that mage is charged the mana cost of the holy word, plus the mana cost of casting counterspell, and the priest doesn't lose any mana since his casting was countered.
Thirdly, the spell would have a willpower based save.
Now, for some examples!
We're going to say Sypher is a GM sorceror, and...I need a volunteer.
*peers around the audience, noticing Thuban hopping up and down in his/her seat like a fish out of water.*
Good, Thuban volunteers. So Thuban is a GM priest from the audience, and Sypher is a GM sorceror with counterspell.
Example Uno
Code:
Thuban starts to concentrate. (Sanctuary)
[HP: 100%] [ME: 100%] [PE: 100%]
twiddle
You patiently twiddle your thumbs.
[HP: 100%] [ME: 100%] [PE: 100%]
c 'counterspell' thuban
You start to concentrate.
Thuban utters the words 'sanctuary'.
Thuban is protected by sanctuary.
[HP: 100%] [ME: 100%] [PE: 100%]
You utter the words 'counterspell'.
Thuban is not casting anything!
[HP: 100%] [ME: 95%] [PE: 100%]
So in example 1(uno) we have Thuban casting sanctuary while Sypher tries to counterspell. Sypher is late with the counterspell however and Thuban succeeds in casting Sanctuary. Sypher is still charged the mana cost for attempting to cast counterspell(IE: 5%).
Example DosCode:
Thuban starts to concentrate. (sanctuary)
[HP: 100%] [ME: 100%] [PE: 100%]
c 'counterspell' Thuban
You start to concentrate.
[HP: 100%] [ME: 100%] [PE: 100%]
You utter the words 'counterspell'.
Thuban's casting has been countered!
[HP: 100%] [ME: 85%] [PE: 100%]
In example 2(dos) we have Thuban attempting to cast sanctuary, Sypher was quicker this time however, and managed to counterspell it. Sypher is charged the mana cost of Thuban's sanctuary spell(IE: 10%), plus the mana cost of counterspell(IE: 5%). Thuban does not lose any mana for the countered sanctuary.
Example TresCode:
Thuban starts to concentrate. (sanctuary)
[HP: 100%] [ME: 100%] [PE: 100%]
c 'counterspell' thuban
You start to concentrate.
[HP: 100%] [ME: 100%] [PE: 100%]
You utter the words 'counterspell'.
Thuban smirks at your failed attempt to counter his/her casting!
[HP: 100%] [ME: 95%] [PE: 100%]
Thuban utters the words 'sanctuary'.
Thuban is protected by sanctuary.
In example 3(tres) Sypher casts counterspell in time to counter Thuban's sanctuary spell, however Thuban makes his/her willpower save, and is unaffected by the counterspell. Sypher is still charged the mana cost of casting counterspell(IE: 5%).
Example QuatroCode:
Thuban starts to concentrate. (holy word)
[HP: 100%] [ME: 100%] [PE: 100%]
c 'counterspell' thuban
You start to concentrate.
[HP: 100%] [ME: 100%] [PE: 100%]
You utter the words 'counterspell'.
Thuban's casting has been countered!
[HP: 100%] [ME: 75%] [PE: 100%]
Thuban starts to concentrate. (holy word)
[HP: 100%] [ME: 75%] [PE: 100%]
c 'counterspell' thuban
You start to concentrate.
[HP: 100%] [ME: 75%] [PE: 100%]
You utter the words 'counterspell'.
Thuban's casting has been countered!
[HP: 100%] [ME: 50%] [PE: 100%]
Thuban starts to concentrate. (holy word)
[HP: 100%] [ME: 50%] [PE: 100%]
c 'counterspell' thuban
You start to concentrate.
[HP: 100%] [ME: 50%] [PE: 100%]
You utter the words 'counterspell'.
Thuban's casting has been countered!
[HP: 100%] [ME: 25%] [PE: 100%]
Thuban starts to concentrate. (holy word)
[HP: 100%] [ME: 25%] [PE: 100%]
c 'counterspell' thuban
You start to concentrate.
[HP: 100%] [ME: 25%] [PE: 100%]
You utter the words 'counterspell'.
Thuban's casting has been countered!
[HP: 100%] [ME: 0%] [PE: 100%]
Thuban starts to concentrate. (harm)
[HP: 100%] [ME: 0%] [PE: 100%]
Thuban utters the words 'harm'.
You moan and vomit as your organs twist!
[HP: 66%] [ME: 0%] [PE: 100%]
Thuban starts to concentrate. (harm)
[HP: 66%] [ME: 0%] [PE: 100%]
Thuban utters the words 'harm'.
You moan and vomit as your organs twist!
[HP: 33%] [ME: 0%] [PE: 100%]
Thuban starts to concentrate. (harm)
[HP: 33%] [ME: 0%] [PE: 100%]
Thuban utters the words 'harm'.
Your body is ripped into bloody chunks by Thuban's spell!
You are dead!
Your eyeball pops out of your head!
[HP: 0%] [ME: 0%] [PE: 100%]
Thuban cackles quietly.
In the example 4(quatro) Sypher has foolishly attempted to spam counterstrike on Thuban. He succeeds in countering all four of Thuban's holy words. However since he successfully countered them, he is charged the mana cost of all of Thuban's holy words(IE: 20% each), and the mana cost of casting counterspell(IE: 5% each), and is quickly run out of mana. Thuban having not lost any mana since all his/her spells were countered, quickly proceeds to destroy the manaless Sypher, who can do little to defend himself.
Anyways, I gave this a good deal of thought before posting it. I think this would be quite a tactical addition to the game for select spellcasters, necros could certainly use it, they could strategically counter holy words and bolts of glory for a limited time that would otherwise just rape them and their entire army. I think with example four I also illustrated how it can't really be abused, especially in solo PK, as the combined mana costs of spells will quickly eat up the casters mana. The caster will have to pick and choose strategic moments to counterspell. It will definitely add an interesting element to group combat, a well placed counter on a heal that might have kept a tank alive could swing a battle.
Thoughts? Comments? Suggestions?