Pokemon from different regions that are similar. Example: Arbok > Seviper
I think I shall list out some:
Patrat-Rattata Galvantula-Ariados Krookodile-Feraligatr Liepard-Purugly Luvdisc-Alomomola Taruros-Bouffalant Chansey-Audino Arbok-Serviper Ursaring-Beartic Pinsir-Heracross Venomoth-Mothim Butterfree-Beautifly Maractus-Cacturne Girafarig-Sawsbuck Aerodactyl-Archeops Pachirisu-Emolga Magikarp-Febass Kingler-Crawdaunt
Here are some of them I know:
Patrat-Rattata Galvantula-Ariados Krookodile-Feraligatr Liepard-Purugly Luvdisc-Alomomola Taruros-Bouffalant Chansey-Audino Arbok-Serviper
This is all I've known! (HOPE THIS HELPS!!!) :)