Casting while in grapple

[Masterbox]

Hey guys,

I got a question for ya all.

Today I was grappled with my sorcerer by a construct with a cmb of 22 and a cmd of 26

So my question now when i want to get in my gasform (Spell lvl 3) how is the DC for the spell calculated?

The Turnorder was set so that it was my turn first and then the construct.

My DM told me that I also had to calculate to my DC throw for concentration the dmg of the round before, which was taken by me.

So is the DC now normal for a grapple situation : 10+CMB+spelllvl.
Or is it: 10+Dmg taken+spelllvl because of the dmg the round before.
Or is it: 15+doublespelllvl because of the defensive cast without an attack of opportunity.

Or is it:
DC 15 (defensice cast)+ KMB (of the enemy, because of grapple)+ double spelllvl (defensice cast) + DMG taken in previous round??

I rly need your help pls.

Because between:

DC 35 (grapplesituation)
DC 13+DMG taken(wounded during casting)
DC 21 (only defensice casting)
DC 43 (defensive+grapple)
DC 43 + DMG taken (defensive+grapple+ wounded during casting)

is a huge difference. And i don´t know which is the right one.

hope u can help me guys. Thx

[Mystic Madness]

Your DM is incorrect concerning the need to account for damage taken last round. The damage inflicted by a grapple is not continuous, as a grapple check must be made every round. It is thus more like an attack than an exposure to a continuous source of damage. Even if grappling did inflict continuous damage, it would be halved for purposes of the concentration calculation.

Also remember that grappled creatures cannot make attacks of opportunity. Thus, unless someone else other than the construct threatens you, you should not need to cast defensively.

The proper concentration check is thus 10 + Attacker's CMB + spell level which equals 35. I believe that if you needed to cast defensively for some reason, that would be a separate check at 21 (15 + 2x spell level)

[Masterbox]

so it is only a normal grapple DC 10+CMB+Spelllvl ?

[Mystic Madness]

Yes. Corrected my original post for spell level. So 35.

[Masterbox]

thank you very very much :D helped me a lot !