Ok so lets say that I have a gnome caster.
He rides a combat trained dog in battle.
to cast while riding him.
First I need to "Guide with knees" DC 5 Ride, Or can I cast with one hand on the reins?
Then I need to make a DC 10+spell Level concentration check due to Vigorus Motion for riding on a dog.
Then if I need to do it defensivly I need to make a DC 15+2xSpell Level Concentration check to cast.
Then I get to cast?
Is that right?
I assume that due to 1's not auto failing the ride can pretend it is not there, Provided I have a +4.
But do concentration checks auto fail?
Sorry for all the Q's, I want to make sure I have all my ducks in a row before game.
I believe one hand is sufficient for casting a spell (see the grappled condition for details), so the first check should be unnecessary.
The only things that "auto-fail"(or "auto-succeed" on nat 20s) are attacks and saves. Everything else is just whatever the total is.
You only need one hand to cast.
Yes for the vigorous motion concentration check. There are feats to help or minimize this. I forget the name of the riding one, but I'm curious enough to look it up.
It's unlikely that you'll be both moving (vigorous motion) and be in melee (for casting defensively), but if so then yes.
Yes.
Sort of.
Dont understand the question.
Still have to roll concentration checks.
no problem.
Casting Spells While Mounted: "You can cast a spell normally if your mount moves up to a normal move (its speed) either before or after you cast. If you have your mount move both before and after you cast a spell, then you're casting the spell while the mount is moving, and you have to make a concentration check due to the vigorous motion (DC 10 + spell level) or lose the spell. If the mount is running (quadruple speed), you can cast a spell when your mount has moved up to twice its speed, but your concentration check is more difficult due to the violent motion (DC 15 + spell level)."
You will not need to guide with knees unless you need both hands.
Ranks in Ride are still recommended, as you want to stay in the saddle if you take damage.
Natural 1 does not fail a Ride check.
Make sure it's a riding dog, not a guard dog, otherwise you may take a -5 penalty to Ride checks as an unsuitable mount (Ask your DM). It may also have the Fighting package instead of the Combat Training package.