If you're running straight Cincinno, you face four main challenges:
1.) Filling the bench rapidly without filling the bench foolishly. In a format with Catcher, simply laying down a multitude of basics is not advantageous as it's handing out free prizes, especially if you bench a single Mincinno.
2.) Addressing being counter-KO'd and damage caps. Cincinno caps at 100 colorless damage. Yanmega is within Pluspower range of this, but Donphan, Reshiram, Zekram, Magnezone, Gothitelle, etc. all have higher HP and the capability to OHKO you with relative ease.
3.) Addressing Donphan in particular. Donphan in particular is a tough matchup for you, winning an attachment on a 1-for-1 basis and are guaranteed at least a 1-for-1 exchange unless you get land prior damage.
4.) Maintaining enough speed to retain momentum for cheap beats in list construction, and against trainer lock.
Finding suitable partners which can address these needs without overly-complicating the deck will pose difficulty. Abomasnow SF would be solid in his ability to answer a lot of these threats in a single tech line, however he's been rotated.
A few solid pointers:
1.) Design your list to retain momentum.
2.) Pack a "nuke" tech that you can efficiently and readily drop.
For instance, if you run Fire in addition to your DCEs, Reshiram makes for a solid (albeit slightly under-damaged) nuke, as he's a single Collector from mobilization (Collector --> Reshi + Shaymin, drop Reshi, drop Shaymin), which means it's a difficult beatstick to stop provided you keep the two fire on board.
If any of the basic Dragons though can pop 120 with an XCC costing, that'd be preferable. I don't know them all of the top of my head, and Reshi makes sense in the context of an above-posted Ninetails list.
