I was SOS chaining Trumbeaks, looking for its hidden ability Pickup, but found a shiny one instead. >.<
I didn't count the chain, but I would guess around 15.
I got this idea from a reddit post, it's a full Baton Pass chain for the purpose of SOS chaining for shinies and hidden abilities. All but the setup lead and end of chain catcher carry Recycle and Leppa Berry so they never run out of PP.
Vangoni - Smeargle
@ Leftovers
[Moody]
- Ingrain
- Substitute
- Double Team
- Baton Pass
Setup passer that provides healing, evasion, a sub to prevent status and another layer of protection, as well as a bunch of stat boosts from Moody. Phazing from Roar/Whirlwind/Dragon Tail/Circle Throw is also prevented by Ingrain.
Shakoni - Smeargle
@ Leppa Berry
[Moody]
- False Swipe
- Soak
- Recycle
- Baton Pass
The idea here is to get the initial Pokémon to 1 HP to increase the chance of it calling for help, as well as later on when you need to switch to the other enemy poke due to the first one nearly running out of PP. Soak allows it to hit ghost types. Moody adds more boosts which are passed to the next Pokémon.
<Japanese name> - Smeargle
@ Leppa Berry
[Technician]
- Icicle Spear
- Entrainment
- Recycle
- Baton Pass
This or the next Smeargle's job is to KO Pokémon and find out their ability using Entrainment (which is also useful for getting rid of Insomnia etc. before catching). Icicle Spear for hitting through Sturdy and types it matches well against, or Aerial Ace on the next Smeargle to hit through evasion and do better against other types.
Artacia - Smeargle
@ Leppa Berry
[Own Tempo]
- Aerial Ace
- Entrainment
- Recycle
- Baton Pass
Farbeagle - Smeargle
@ Silk Scarf
[Technician]
- Spore
- Hold Back
- Aerial Ace
- Soak
The catcher which I've been using during my playthrough, which will end the chain.
I also have a False Swipe Decidueye for Riolu and other fighting types that use Final Gambit, being immune to most of their moveset due to the ghost type. A Damp Parasect for catching exploding Pokémon is most likely the next Pokémon I will make.
If anyone needs help teaching Smeargle any move just ask. The only problem move was Baton Pass which required me to use wild Ditto to learn the move by transforming into one of my Pokémon (that only knew Baton Pass thanks to the move deleter) and then switch to Smeargle and sketch it.