Imma make a bold prediction and say that Ash gets a Noibat and uses it VS Valerie's Spritzee. That'd sorta justify Spritzee being Valerie's ace, they're pretty evenly matched size wise and it'd have the classic type disadvantage flavour added as well. The Noibat in the Pikachu Short was placed apart from the other "random" mons in the cast list right? Might belong to the main cast.
Could still be Fletchinder but even then Spritzee looks weak in comparison imo. (though a Bellsprout/Tynamo scenario is of course possible)
But that would mean he has three flying types...
I think his next Pokémon could be Skiddo or Carbink and his last one is a Bergmite.
Vs. Valerie
Skiddo/Carbink vs. Mr. Mime (Mr. Mime)
Fletchinder vs. Mr. Mime (Fletchinder)
Fletchidner vs. Sylveon (Fletchinder recalled)
Frogadier vs. Sylveon (Frogadier)
Frogadier vs. Mawile (Mawile)
Fletchinder vs. Mawile (Fletchinder evolves)
Talonflame vs. Mawile (Talonflame)
Vs. Olympia
Bergmite vs. Sigilyph (Bergmite)
Bergmite vs. Slowking (Slowking)
Pikachu vs. Jynx (Draw)
Gogoat/Carbink vs. Slowking (Gogoat/Carbink)
Gogoat/Carbink vs. Meowstic (Meowstic)
Hawlucha vs. Meowstic (Hawlucha)
Vs. Wulfric
Frogadier vs. Cryogonal (Frogadier recalled)
Hawlucha vs. Cryogonal (Hawlucha)
Hawlucha vs. Beartic (Beartic)
Bergmite vs. Beartic (Bergmite)
Bergmite vs. Cloyster (Bergmite recalled)
Pikachu vs. Cloyster (Pikachu)
Pikachu vs. Abomasnow (Abomasnow)
Frogadier vs. Abomasnow (Abomasnow)
Talonflame vs. Abomasnow (Talonflame)
Talonflame vs. Aurorus (Aurorus)
Gogoat/Carbink vs. Aurorus (Gogoat/Carbink)
Gogoat/Carbink vs. Avalugg (Avalugg)
Bergmite vs. Avalugg (Bergmite evolves)
Avalugg vs. Avalugg (Ash's Avalugg)