Here’s what I found on Bulbapedia.
Team Rocket’s Meowth (obviously)
Ash and Team Rocket’s Pokemon in “Island of the Giant Pokemon”
The Tentacruel in “Tentacool & Tentacruel”
The Gastly in “The Ghost of Maiden’s Peak”
The Lapras in “Holiday Hi-Jynx”
The Haunter and Gastly in “A Shipful of Shivers”
The Slowking in “The Power of One”
The Ninetales in “Just Waiting On a Friend”
The Larvitar in “Address Unown”
The Ralts in “Do I Hear A Ralts?”
The Lucario in “Lucario and the Mystery of Mew”
Chatot (repeats what people say in multiple episodes)
The Zorua in “Zoroark: Master of Illusions”
The Yamask in “A Night in the Nacrene City Museum!”
The Zoroark in “The Island of Illusions!”
The Beheeyem in “Capacia Island UFO!”
Mirror World Meowth in “The Cave of Mirrors!”
The Diggersby, Pangoro, Delphox, Froakie, and Chesnaught in “Dream A Little Dream from Me!”
Rotom Dex throughout the SM saga
Ash’s Pikachu in “I Choose You!”
Ash and Goh’s Rotom phones throughout the Pokémon Journeys series
Source
Hope this helps! :)
