I could see Infernape for Gary honestly. And he was in Sinnoh for a good bit of time.
I'm curious because of the random Infernape in the OP. Unless Ash's comes back, Gary seems like the most likely character for it to appear alongside. It could be an interesting matchup for Lucario.
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While you will usually see Goh's pokemon interacting in the background at Sakuragi park, there are a couple that that have evaded any kind of appearance, with small Magicarp only recently leaving the "Did the writers forget Goh caught them?" jail.
Excluding Suicune who is roaming, Pokemon of Goh's that haven't been seen since they were caught/ evolved are:
Morelull, # of days since Morlull was first (and last) seen: 54
Drowzee, # of days since Drowzee was first (and last) seen: 68
Diglett, # of days since Diglett was first (and last) seen: 75
Arctozolt, # of days since Arctozolt was first (and last) seen: 89
Greedent, # of days since Greedent was first (and last) seen: 131
Hitmonchan, # of days since Hitmonchan was first (and last) seen: 227
Binacle, # of days since Binacle was first (and last) seen: 290
If you have spotted one of these elusive pokemon, please let us know.