Casting while Mounted Questions...

[Pugnacious Twiddlebury]

A character (a small gnome let's say) wants to cast a spell from the back of his large mount in combat..
What are the ramifications?
Does it provoke an AOO?
Can the AOO be avoided with a Feat, Ride Check, or other Maneuver?

I understand that if the Mount makes a FULL attack there is a Concentration Check involved.

I guess it might be easier to drop off the back of the mount and use it as cover... but it doesn't really look as cool.

Separate but related question:
Can the rider use a reach weapon even if the mount is adjacent to the target?

[FrodoOf9Fingers]

You are considered to be sharing all of the spaces as your mount. So if you cast a spell, and the mount your on is in a threatened square, then you will provoke.

You can avoid the AoO by casting the spell defensively (as usual).

[Pugnacious Twiddlebury]

So assuming you are in full combat mode.. casting flaming death on the enemy while your fearless mount tears into them with full attacks.. you are making 2 concentration checks a round no matter how good or bad a rider you are?

And there is no way to put the large mount between you and the threatening critter.. even though the mount is 2 sizes larger than you are?

[FrodoOf9Fingers]

Yep :), one for the motion, and the other to not letting your guard down (spell casting takes TONS of concentration O.o)

[Pugnacious Twiddlebury]

So it's going to take like 3 feats to fix this.
Combat Casting
Uncanny Concentration
Additional Traits (including Desperate Focus or Focused Mind)

Hmm.. that's +8 to your Concentration roll.
So assuming you are Level 1 with a +3 stat...
1d20=1 roll+8 feats+1 level+3 stat=13
Doesn't quite get you to 'always succeed' on a DC 17 Concentration roll.

At level 9 with a +6 stat...
1d20=1 roll+8 feats+9 level+6 stat=24
DC for level 5 spells is 25 so you are almost there...

At level 20 with a +8 stat...
1d20=1 roll+8 feats+20 level+8 stat=37
DC for level 9 spells is 33, so you are good at that point... but not by a huge margin.

What's the effect of a 1 on a Concentration roll?

[DesolateHarmony]

A concentration roll is an ability check, not a saving throw or an attack roll. Saving throws and attack rolls both specify automatic failure on a 1, and automatic success on a 20. Not other kinds of rolls.

[Xanzal]

Keep in mind that with Uncanny Concentration, you stop worrying about vigorous/violent motion. Such as riding on a mount. Then you're down to just casting defensively.

[Pugnacious Twiddlebury]

The violent motion roll rapidly becomes moot actually...
since you only need to make a DC of 15 + SL x1 for Violent Motion but you need a DC of 15 + SL x2 for Casting Defensively.

[Pugnacious Twiddlebury]

Oooo.. Gloves of Elvenkind for the win!
Apparently these should be called RIDING Gloves of Elvenkind! +5 to Concentration Checks to Cast Defensively!
Doesn't help with the violent action... but if you get Uncanny Concentration you don't need to make that roll anymore.