You can add your Mastery Ability score to any Concentration rolls you must make after casting the spell. As an added benefit, when you stop Concentrating, the spell can continue (if you choose) after you stop concentrating for up to as many rounds as you have ranks in Mastery for the spell. The spell will continue doing what it was doing when it ended. A floating object will coninue floating and/or travelling in the direction it was headed when the wizard stopped concentrating for example.
1- Concentration: You may add your Mastery Ability score to any Concentration rolls you must make to allow the casting the spell.
2-Lasting Effect: As an added benefit, when you stop Concentrating, the spell can continue (if you choose) after you stop concentrating for up to as many rounds as you have ranks in Mastery for the spell. The spell will continue doing what it was doing when it ended. A floating object will coninue floating and/or travelling in the direction it was headed when the wizard stopped concentrating for example.
I like the concentration bonus. the lasting effect seems a bit out of reach of a mastery ability. I think I would even have it as a house rule where every rank in mastery grants a bonus to concentration rolls (No need of a specific rank in concentration).
I'm not sure if its too much really. When comparing the lasting effect with such effects like Multi Casting, Fast Cast, and Penetration, it about balances out. I think those 3 are a bit more powerful, even though they only do one thing, where this provides two benefits. The first benefit is not all that significant either considering that most Magi won't raise their Mastery abilities to great levels. I doubt a Magus would get more than 3 rounds of the spell continuing. For a greater similar benefit they would use Maintaining the Demanding Spell.
The bonus of Mastery to Concentration rolls for that spell is a huge benefit on itself. It allows you to do other things (like defending, dodging, talking, running or casting another spell) while concentrating.
I myself would modify the Lasting effect: It allows you to maintain spells for longer duration. Propably adding 5 minutes per Mastery rank to the maximum duration you can keep a concentration spell on (which is 15 times Concentration ability score). It will not allow you to Harness the spell allowing it to continue its existence after you stop concentrating on it.
The latter modificatin would change the maximum duration for Concentration to 15 times Concentration score + 5 times Mastery (if the user has Concentration mastery).
I agree with william that the lasting effect seems a bit out of reach of the mastery ability, not because it's overly powerful, I just don't see as part of a mastery of concentration.
William wrote:
I think I would even have it as a house rule where every rank in mastery grants a bonus to concentration rolls (No need of a specific rank in concentration).
I think this is going too far and prefer having it as a seperate ability.
I really like Kautsu's alternative to the lasting effect.