I think the spells should work like Shadow Conjuration and Greater Shadow Conjuration. A single spell that can mimic the effects of several other spells.
This is due to the fact that curses are supposed to be able to take an INFINITE number of possible shapes.
I also believe that curses enable a great means by which players can interact, either by Sharing a curse, or by one Player-Character placing a Curse over another.
I believe the spells should remain the same level, due to the fact that none of the effects produced by either is more powerful than an effect of equal or lower spell level, which is a very widely accepted rule by Dungeon Masters in regards to the Bestow Curse spell.
Essentially: Bestow Curse workds like a very low-level equivalent of a "Wish" spell. You name a desired outcome and as long as it's no more powerful than a spell of the same level or lower it should reasonably be allowed.
Here is how I think the spell should look:
Bestow Curse
Sor/Wiz 4 Cleric/Bard 4
Components: V,S,M
Casting Time: Standard Action
Duration: Permanent
When you cast Bestow Curse Choose one of the following Modes:
-Blindness (As the Spell)
-2 to all ability Scores (( Standard mode))
-Slow (As the Spell)
- Charm Monster (As the spell)
-Ray of Enfeeblement (As the spell)
This also gives players a means by which to Roleplay a "Charmed" Character who has been charmed for the long-term. For example, this gives a means by which a PC could cast Charm Person on another PC in order to exact their help in a long-term plan.
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Greater Bestow Curse:
Sor/Wiz 8 Bard 6
This spell works like Bestow Curse, except choose the following options:
Hold Monster (As the Spell)
Baleful Polymorph (As the Spell)
Dominate Person (As the Spell)
Greater Sanctuary (As the Spell. Works like Bard's Haven Song, except only the Target can't attack you until the curse is removed. Ends if you attack them.)
-6 to all Ability Scores (Standard mode)
This also enacts the ability for a player to roleplay Long-Term Domination of another player. This is a common tactic of Dominate Person spells. If you read Return to Castle Ravenloft Baron Strahd von Zarovitch has a woman dominated over the course of several days, forced to "act normal" until he tells her otherwise.
This adds a mechanical way and RP way for a player to also install things such as "Sleeper Agents." Agents who don't know they are Dominated until "activated."
To be more specific: This also gives a means by which to enact the effects of the spell "Geas/Quest." Where you force a player to go on a quest for you.
The reason for this is because Geas/Quest can be removed with Bestow Curse.
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Secondly: I believe that there should be a Remove Curse and Greater Remove Curse spell, just as there are Dispel Magic and Greater Dispel Magic. And I think that Remove Curse should require a caster level check to dispel a Curse the exact same way a Dispel Magic should be rolled against dispelling a spell.
I do not know if this is possible, or if it is "Hard coded" into the game, but I just think from both a Mechanical and a Roleplay aspect that a 5th level Cleric casting a 3rd level spell should not be able to remove the curse of a 30th level Sorceror/Wizard.
Forcing it to have a Caster Level check also means that Clerics at Temples MAY NOT automatically succeed at removing a curse.:
This can also add the extra bit of roleplay fun of having to locate a means to remove a powerful curse placed upon you by a powerful PC...especially if part of that Curse is that they can control you at any time!!!
Just my thoughts, and as always I appreciate Feedback!!!