Separating them is fine if you prefer. Something like this?
Additional Special Abilities
An undead dragon slayer may select [any 4?] of the following special abilities.
Anti-Dragon Evocation (Sp): 3 times per day, an undead dragon slayer may alter any evocation spell they cast so that it does an extra 50% of force damage against dragons. For example, a caster level 10 fireball does 10d6 hp of fire damage, plus an additional 5d6 points of force damage to dragons. Anti-dragon force damage stacks with Metamagic feats that increase a spell's damage: e.g. a CL 12 Empowered flame strike would do (12d6 increased by 50%) fire damage, plus an additional 9d6 force damage to dragons.
Bind Wings (Su): Once per day, an undead dragon slayer may spend a full attack action to make a single attack imbued with the ability to bind a dragon's wings. If the attack hits a creature with the dragon subtype, bands of force wrap around the dragon, preventing flight for 1d6 rounds. If the dragon is in flight at the time that this ability takes effect, the dragon falls immediately, taking falling damage (unless prevented by a feather fall spell or similar ability). The bands of force are immune to damage and cannot be burst by Strength checks, but they can be destroyed by any effect that can destroy a wall of force. A bound dragon may escape with a successful Escape Artist check (DC equals 10 + undead dragon slayer's HD + undead dragon slayer's Cha modifier).
Dazzling Display (Su): As a standard action or part of a full attack action, an undead dragon slayer may make a series of complicated motions with its weapons which befuddles any dragon that sees it. Any dragon within 120 feet that can see the slayer must make a Fortitude save or become dazzled for 1d6 rounds. In addition, the dragon must make a Concentration check to cast any spell, use a spell-like ability, or maintain a spell that requires Concentration (DC equals 10 + undead dragon slayer's HD + undead dragon slayer's Cha modifier). If the dazzling display is part of a full attack action, all attacks take a -2 attack penalty.
Enchant Dragon (Sp): 3/day an undead dragon slayer can alter an Enchantment spell that usually has no effect on dragons, such as charm person, so it will affect dragons as if they were the type of creature the spell is most effective against.
Improved Breath Evasion (Ex): The undead dragon slayer gains improved evasion (as the rogue class feature) against breath weapons.
Scry Dragon (Sp): 3 times per day, the Undead Dragon Slayer can modify any divination spell so it is especially effective against dragons. The spell gains a +1 bonus on caster level checks to overcome a dragon's spell resistance and its range increases by 100%. These adjustments stack with spell augmentations from other sources, such as the Spell Penetration or Enlarge Spell metamagic feats.
A spell modified by scry dragon is only capable of detecting dragons. Thus a modified detect evil spell is able to detect evil dragons to a 120 ft. range, but cannot detect evil creatures that are not dragons. Scry Dragon can only modify divination spells that are capable of detecting dragons or phenomena of a draconic nature. It could not modify locate object (since dragons are not objects), but could modify detect undead or detect thought (to detect an undead dragon or a dragon's thoughts).
Smite Dragon (Su): Once per day, an undead dragon slayer may attempt to smite a dragon with one normal melee attack. She adds her Charisma bonus (if any) to her attack roll and deals 1 extra point of damage per HD. If the paladin accidentally smites a non-dragon, the smite has no effect, but the ability is still used up for that day.
Transmute Dragon (Sp): As Enchant Dragon (see above), except it alters a Transmutation spell, such as reduce person, so it affect dragons.
True Strike (Sp): The undead dragon slayer may use true strike once per day as a move action on any attack against a dragon.
Improved Additional Special Abilities
For every 2 points of BAB above +11 or 2 levels of caster level above 11th, the undead dragon slayer may choose one of the following special abilities (or one of the "additional special abilities" listed above). To choose an improved ability, the undead dragon slayer must already possess the corresponding special ability given above.
Improved Dazzling Display (Su): The undead dragon slayer may make a dazzling display as part of a standard attack action or a full attack action, and the dazzling display DC gains a +2 enhancement bonus (see Dazzling Display above). To select this special ability, the undead dragon slayer must already have the Dazzling Display special attack.
Improved Dragon Defense (Ex): The undead dragon slayer gains an additional +2 dodge bonus to AC and a +1 bonus to Reflex saves against attacks made by dragons, which stacks with Dragon Defense.
Improved Weapon Throwing (Ex): An undead dragon slayer can throw any weapon as an attack against a dragon. The attack does not take any penalties for being an improvised weapon but instead gains a +4 racial attack bonus and does additional damage equal to 1d6 plus 1d6 per 2 HD of the undead dragon slayer. The attack bonus does not stack with that gained from the Weapon Throwing ability.
I think there are one or two easy improvements to Anti-Dragon Casting, but I'm not so sure about some of the others.
