So a level 10 character can cast this with a 4 level spell.
the DC could be
10+4(Spell level)+6(Int)+2(Greater spell focus)=22
If the target tries to cast a level 5 spell the DC would be 26.
If the target is level 10 as well it would have a bonus of. 10(Level)+6(int)
So a 50% chance of making the save.
I'm guessing that the chance will stay around that at earlier or later levels.
Yeah, but the spell also has to affect them, and of course a solid mid-level spell which affects a spellcaster may well be able to stop them casting spells anyway. I'm not saying it's useless - a spell like disruptive ice storm might be useful in the right situation - but you might find that a hold monster spell or something would work better.
Also remember that there are items which can boost concentration checks. They're rare on NPCs, true.
Yeah, but the spell also has to affect them, and of course a solid mid-level spell which affects a spellcaster may well be able to stop them casting spells anyway. I'm not saying it's useless - a spell like disruptive ice storm might be useful in the right situation - but you might find that a hold monster spell or something would work better.
Also, remember that there are items which can boost concentration checks. They're rare on NPCs, true.
Looking for a meta-magic feat to add to greater dispell magic. I did not find many that are fun and good :(