Cleon
Legend
Updated, finally!
I think the SAs' wording needs some slight tweaking:
Anti-Dragon Casting (Ex): Undead dragon slayers gain a bonus equal to half their favored enemy bonus on caster level checks to overcome the spell resistance of dragons (this does not stack with other bonuses, such as from the feat Spell Penetration) as well as the benefits of the Spell Focus feat for all spells cast against dragons. At caster level 17th, an undead dragon slayer also gains the benefits of the Greater Spell Focus feat for all spells cast against dragons.
Favored Enemy (Dragon) (Ex): Undead dragon slayers have dragons as favored enemies, as per the ranger class ability. The bonus is equal to the maximum bonus achieved by a ranger of the dragon slayer's HD. An undead dragon slayers' favored enemy (dragon) ability does not stack with any other favored enemy ability.
The current Smite Dragon is very weedy (just compare it to the Improved Weapon Throwing) and still has a "paladin" in it.
Indeed, the damage is very weak compared to the Favored Enemy bonus of +1 per HD.
I suggest making this a "Dragon Strike" ability with some different bonuses, such as an improvement to hit. Then add Improved Dragon Strike as an optional extra.
e.g.:
Dragon Strike (Ex?): X times a day, as a standard action, an undead dragon slayer can make a single attack against a dragon with an insight bonus to the attack and damage rolls equal to the slayer's Hit Dice (maximum +20). Additionally, a dragon strike attack is not affected by the miss chance that applies to attackers trying to strike a concealed target (provided the target is a dragon).
Improved Dragon Strike (Ex?): 3 times a day, as a swift action, an undead dragon slayer can add an insight bonus equal to their Hit Dice (maximum +20) to the attack and damage rolls of their next attack against a dragon (if it is made before the end of the next round). Additionally, a dragon strike attack is not affected by the miss chance that applies to attackers trying to strike a concealed target (provided the target is a dragon).