In all Mainstream Pokemon Games, there will be a number of Non-Playable Characters looking to Trade Pokemon with your trainer. Some of these trades are for really good Pokemon that can't be found in the Wild otherwise, while a few aren't all that worth it since these Pokemon can easily be found. In all, there are nine different In-Game Trades available for your trainer.
Available In-Game Trades
Mr. Mime: In one of the houses on Route 2, you will find a trainer looking to Trade you their Mr. Mime. They will request an Abra in return. Since Mr. Mime cannot be found in the Wild, this trade is a must.
Jynx: In one of the houses in Cerulean City, you will find a trainer looking to Trade you their Jynx. They will request a Poliwhirl in return. Since Jynx cannot be found in the Wild, this trade is a must.
Nidora Female / Nidoran Male: In the entrance to the Underground Tunnel on Route 5, you will find a trainer looking to Trade you their Nidoran Female (FireRed) / Nidoran Male (LeafGreen). They will request a Nidoran of the opposite gender. Nidoran can easily be found in the Wild, so pass on this trade.
Farfetch'd: In one of the houses in Vermilion City, you will find a trainer looking to Trade you their Farfetch'd. They will request a Spearow in return. Since Farfetch'd cannot be found in the Wild, this trade is a must.
Nidorino / Nidorina: In the gate on Route 11, you will find a trainer looking to Trade you their Nidorino (FireRed) / Nidorina (LeafGreen). They will request a Nidorina (FireRed) / Nidorino (LeafGreen) in return. Both of these Pokemon can easily be found in the Wild, so pass on this trade.
Lickitung: In the gate on Route 18, you will find a trainer looking to Trade your their Lickitung. They will request a Golduck (FiredRed) / Slowbro (LeafGreen) in return. Since Lickitung cannot be found in the Wild, this trade is a must.
Seel: In the lab on Cinnabar Island, you will find a trainer looking to Trade your their Seel. They will request Ponyta in return. Since Seel can easily be found in the wild, pass on this trade.
Electrode: In the lab on Cinnabar Island, you will find a trainer looking to Trade your their Electrode. They will request Raichu in return. Since Electrode can easily be found in the wild, pass on this trade.
Tangela: In the lab on Cinnabar Island, you will find a trainer looking to Trade your their Tangela. They will request Venonat in return. Since Tangela can easily be found in the wild, pass on this trade.
Now that you know all about the available In Game Trades, Click Here to learn about what Interactable Pokemon you will find during your journey!