As far as I know, something like this has been attempted before, but there have been a lot of rule discussions regarding mounted combat and Aid Another bonuses that I hope to have grasped enough to come up with a legit concept. I've read countless threads on various message boards and I'm sorry that a) none of this is actually new and b) I didn't think of remembering the names of other contributors on whose shoulders this brave little man finds himself:
This concept is for a supporter/buffer Halfling Dragon Cavalier based on synergies between teamwork feats, mounted combat, traits and the Honor Guard archetype for the Cavalier. I will only use Paizo-created content, but may point out 3rd-party stuff. Multi-classing is also avoided as the possibilities are limitless, the stack interferences even more so and the powerful Cavalier abilities should, in my opinion, have the chance to grow.
First things first. The Aid Another action is usually a standard action until modified by, e.g., the Bodyguard feat. It grants your ally/allies certain bonuses to their actions, in combat (mainly, but not exclusively) bonuses to AC against one attack or to attack on the ally's next attack. Out of combat, skill checks are pushable as well. Buffing saving throws is a vague topic, but let's assume that saves against ongoing effects can also be Aided in and out of combat. With appropriate roleplay and readied actions a GM might even rule buffing instantaneous saving throws as legit. One poster gave the example of pulling back a rogue tied to a rope as soon as a trap goes off (buffing reflex). Another example might be startling an ally subjected to a sleep effect or a pep talk against a fear effect.
So what the Halfling Dragon Honor Guard (HDHG from now on) can do each round is help somebody else be a better attacker or to raise survivability at the cost of your own standard action and a check with DC 10. This ally can indeed be your mount, as being adjacent is a prerequisite for only some instances and this "adjacency" is given when you are within 5ft. distance (ask your GM, but limiting this to adjacent grid fields is a) not what the rules say adjacent (as a one word term) means, and b) punishing a team player who might as well have played a charger or even another class).
Aiding your mount is a nice way of being able to ride/fly solo or when you find that nobody is in direct reach or dire need. It's just not you but your mount that is doing the actual ass-kicking.
Aid Another is modified by a large number of mechanics in this build. So we have to be certain about what stacks and what doesn't from wording. This has often been the reason for heated discussions and needs to be gone through thoroughly with your GM.
Improving the Aid Another bonus: We start out with a base one-time +2 bonus to AC, attack, a skill check or a save. The racial trait Helpful (Halfling) increases this to a base +4 bonus. Alternatively, the Dragon Cavalier's 2nd-level Aid Allies class ability increases the +2 to a base +3, with a +1 increase on levels 8, 14 and 20. Why take both when they don't stack? Because one is only a trait and other traits that might stack with Aid Allies exist, but are usually highly situational. On the other hand, a +4 bonus at the first few levels is way more powerful than waiting for it until level 8. The Dragon Order is also useful for other stuff, so we'll just accept that the flat +4 bonus from level 1 increases to a flat +5 at level 14.
This +4 bonus isn't the end of it yet, but the other boosts are situational.
Boosting AC: To boost the +4 to AC further, we take the Honor Guard archetype that grants us the Bodyguard feat through the 3rd-level Intercept class abilty and, on top, a +1 increase to our +4. If we add the archetype's 1st-level Sworn Defense challenge ability modifier (íssue a challenge, select one ally as your ward for the duration), your ward also gets a +1 dodge bonus to AC. With a higher-level bodyguard mount that also qualifies for the Bodyguard feat, you and your mount can work together to add another +2 on top. Cool thing? Bodyguard lets you do this by spending one of your attacks of opportunity as an immediate Aid Another action. So, as long as you and your mount beneath you are adjacent to your ward during a challenge and both of you win the DC 10 check, this ward gets a +8 AC against as many attacks as you and your mount have AOOs. If you haven't challenged anyone, this still is a +7. Should you fly solo, you can grant your mount your +5 and your mount supports your AC with +2 by solely spending AOOs. Guess why both of you should not neglect your Dexterity modifiers and get the Combat Reflexes feat even if you both don't actually need it to get Bodyguard? Both the bodyguard animal companion and an Honor Guard could get Bodyguard without having to meet the requirements. In the Pathfinder Player Companion: Melee Tactics Toolbox we find the Harrying Partners (Combat, Teamwork) feat which might make Combat Reflexes a bit less necessary as you can grant it to a large number of allies with your greater tactician class ability on 9th level. The feat extends the Aid Another bonuses you and your allies provide to the beginning of each Harrying Partner's next turn. That way not only one adjacent ally gets your bonus to AC against one attack per AOO spent. It's actually one adjacent ally per AOO spent that gains that bonus!
Another way to boost AC is the Saving Shield feat with which you can raise an ally's AC +2 against one attack with an immediate action (I can't find anywhere what kind of action an attack of opportunity is. Ask your GM if Bodyguard and Saving Shield stack).
Boosting attack rolls: When riding solo on your mount (at first level probably a wolf), you could bolster your mount's attack in the following ways: If you together charge (+2 attack, -2 AC) a challenged enemy, your mount gets a +1 circumstance bonus to her attacks (+1 for every four Cavalier levels) from your challenge, as well as a +1 morale bonus from your 5th-level Banner ability. When you also Aid Another as a standard action, your mount gets a total of +8 (at level 3) on top of her normal modifier if she makes one attack at the end of the charge, or alternatively you could direct her in her trip attempt for a +4 on CMB. This does not preclude boosting the mount's AC per Bodyguard as well if it should get hit. When in melee, you and your mount can both boost one attack (or more per Harrying Partners) of an ally by providing a flank bonus once (+2), the +2 of your mount's Aid Another as well as your +4 Aid Another bonus. Should you have challenged the enemy, your ally gets additional bonuses from your Dragon Order Challenge, so we're talking about a combined +9 minimum at first level for an ally's attack that absolutely needs to hit. If we include the Harrying Partners one-round extension, multi-attack classes like TWF, Magi, etc. will love you a lot. The fun increases if you all decide to get Outflank (Combat, Teamwork) independently, as sadly your 9th-level greater tactician feat is Harrying Partners, for another +2 on attack and your multi-attack ally starts critting. All the attack shenanigans demand you to have exactly the same reach as your mount, so maybe a scimitar until your wolf becomes large at level 7 and you can use that lance. Also don't forget that beginning at 5th level, charging allies get a +1 morale attack bonus within 60ft, should you be able to position yourself well so that your ally can charge into flanking position for a total of +14 (including Outflank, both you and your mount Aiding, and the enemy being challenged).
Boosting saves: Your HDHG can also do wonders for your allies' saves. Not only can you Aid Another, but with the feat Lucky Halfling, one of your allies per day can profit from a reroll with your bonuses. As your constitution and your dexterity scores are already rather high and you have the racial ability Halfling Luck for a +1 on all your saves, your saving throw might potentially (drumroll) save your ally. Against fear effects this gets even more ridiculous, as you yourself get an additional +2 from that racial ability as well as another +2 with a banner flying beginning at 5th level, and all that within 30ft (Lucky Halfling) or 60ft. (Banner). If your GM is nice and you can Aid Another one's instantaneous saving throws with a readied action, just add another +4 to the original save (+2 if your mount does the same). With the teamwork feat Shake It Off taken with tactician at first level, this (independently from anything else discussed here) adds another +2 to any one's saving throw if you and your mount are adjacent to an ally and you fire off tactician.
Boosting skill checks: As you need only crack a DC 10 to Aid Another, all kinds of skill checks may benefit from you (and your mount) being around. This touches heavily on role playing and potentially borders on ridiculousness repeatedly, but any skill that can be used untrained is already a no-brainer: your ally wants you and your mount (intelligence raised to 3 at 4th level provided) around to help out for a potential +6 to a check. Any skill that needs to be trained might be worth it to invest at least one skill point for the Cavalier. You could easily play the “good cop” in interrogation scenarios, the spin doctor in diplomatic encounters, as well as the second pair of eyes staring into a bluffer's face for clues. The halfling or even an intelligent mount could play assistant for all kinds of crafting jobs (holding picklocks, working the bellows, taste-testing potions or spirits), having invested one skill point, of course.
Many abilities from the Honor Guard haven't even been mentioned yet, as well as the Dragon Cavalier's strong perception and survival skills. But the guide is already quite substantial. Also of note are the Benevolent weapon and armor/shield enchantments that, at a rather low additional price, add the weapon's enhancement bonus to Aid Another when supporting an ally's attacks or the armor/shield's enhancement bonus on AC.
recommended feats:
HDHG
1st level (regular) Combat Reflexes
1st level (tactician) Shake It Off
3rd level (Honor Guard) Bodyguard
3rd level (regular) Lucky Halfling
5th level (regular) Saving Shield
7th level (regular) Outflank
9th level (regular) Improved Critical (lance) or (scimitar)
9th level (greater tactician) Harrying Partners
additional interesting feats (to taste):
In Harm's Way (You have decent HP)
Mounted Combat
Shield Focus
Mounted Shield
Ride-by Attack
Spirited Charge
mount (bodyguard)
1st level (regular) Combat Reflexes
2nd level (regular) Bodyguard
5th level (regular) Improved Natural Attack (bite)
8th level (regular) Outflank
additional feats (to taste):
Weapon Focus (bite)
Narrow Frame (if still wolf after 6th level)
Power Attack
Dodge
Mobility
Medium Armor Proficiency
In Harm's Way
Conclusion
With this character, you can be a competent supporter to other classes, mainly in melee. Your damage-dealing abilities might be negligible at first, but even that changes around level 10 to an at least satisfying level. Indeed what this concept promises is a large variety of situations in which you can make your allies' lives easier and a large number of roles you can play in and outside of fights. As your abilities are not magic-based, they are not dispellable and with many of them you do not run out of uses per day. What is even more positive is the whole outlook of this concept, because it is eager to please and quite fitting to a halfling. Only similar bonuses from other classes that don't stack with yours might be a nuisance, be it the Bard's Inspire Courage bardic music or the Paladin's 10ft.-radius Aura of Courage. But even then more things might stack than not, as Aid Another gives an unspecified bonus. This concept can also suit different player attitudes, from outgoing to introvert, from lawful good to chaotic neutral (this whole concept is the opposite of evil and halflings as well, but even then you could play a slaver's assistant or an evil mage's lackey).
I'm looking forward to feedback and hope you like it!