So, I've been tinkering around with Concepts That Should Not Be Considered(tm) and one of my thoughts is that I wanted to make a ninja who has an imperial dragon-esque eidolon as a special "summoning jutsu". I know that most folks would go "Uh, no" at the thought of a multiclass summoner concept, but... for kicks, I'd like to see if folks can come up with something (and if they can, I will steal it shamelessly and use it for a kickass character).
For my part, I'll say that I start off with 2 levels in Ninja, grabbing Weapon Finesse, Sneak Attack and using a Combat Trick to take Two-weapon Fighting and get the most out of my attacks. By level 3, grab a level in Summoner and introduce my imperial dragon to the fray (Serpentine base, claws and extra limbs (legs) as my primary evolutions). Probably take another level in Summoner and then grab another level in Ninja to up my Sneak Attack damage. After that, I'm thinking that I should take 2 Summoner levels, a level in ninja, and repeat until level 20 (that should give me 12 Summoner levels and 8 Ninja levels, if I've done my math right).
Any other suggestions? I know it's not optimal, but some concepts are entirely too awesome to not at least try and make work.
You wouldn't have to go Ninja to be a "ninja", honestly an unchained rogue would ease up on the MADness of the build your thinking. Allowing for Dex to damage, and free weapon finesse, if from summoner all your looking for is the Eidolon to have your "Imperial Dragon" why not just VMC into Summoner to get the Eidolon?
If your going Summoner for a small list of spells, seeing by level 12 your not doing much in terms of higher then 6th level spells anyway, just go with Phantom Thief to get Major magic a ton, and cherry pick the Wizard list. Not enough spells? Eldritch Scoundrel and you have tons of spells now.
Single-class Magical Child Vigilante. Your Familiar doesn't start out as a Dragon, but eventually it can morph into a Pseudodragon. If this is too small, use VMC Summoner and have the Familiar "morph" into the Eidolon by being inside it when the Eidolon is summoned (conveniently, the Eidolon comes online at the same time your Familiar morphs into a Pseudragon; ask your GM if you can have the Eidolon work like that of a Synthesist Summoner, except that it goes on your Familiar instead of you; otherwise, flavor it as your Familiar summoning a greater spiritual avatar of itself). The downside: Regardless of whether your GM is nice to you, your Eidolon is rather wimpy, because VMC Summoner is rather bad.
If you want to concentrate more on being a Ninja (actually Rogue), use Eldritch Scounndrel Rogue VMC Summoner. Eldritch Scoundrel can even take Ninja Tricks and sacrifice spell slots to power them. The downside: VMC Summoner is still rather bad.
If you really want to concentrate on the Summoner part and have some Ninja (actually Rogue) abilities on top of it, go Summoner VMC Rogue (eventually get Sneak Attack) or alternatively Summoner VMC Monk (eventually get a limited amount of Ki Power, although warning in advance: this VMC is normally rather bad). Unfortunately, no VMC Ninja is available. On the plus side, the Summoner-based approach avoids the problem that VMC Summoner is rather bad (as noted above). The down side is that VMC Monk is rather bad except in very specific builds, and this isn't one of those exceptions, while VMC Rogue is okay but doesn't give you much Ninja flavor (you will have to use spells to fill some of that in).
On the plus side for all 3 builds above, none of the VMCs mentioned above are as bad as VMC Witch or VMC Gunslinger.
As Gestalt, this'd be a lot of fun since your Eidolon wouldn't fall too far back to the equivalent threats you would face, and the two of you could be Wombo-Combo bros juggling opponents together. The synergy is nice because the Eidolon would help enable your sneaks to land, especially if your Eidolon wasn't DPS-focused as much as a CMB-wrecking machine.
The image I get from this is akin to those Naruto fighting games. Complete with the unnecessary internal and vocal monologues taking place throughout the fight between yourself, your Eidolon, and the enemies.