In Unstuck in Time, starter Pokémon is a shorthand term for a player character's first Pokémon. All starter Pokémon are level 5 and do not have TM or egg moves. In the case of species that can have different abilities (excluding Dream World abilities) or that could have learned more than four moves by level 5, ability and moveset are randomly selected (with at least one damaging move guaranteed when possible).
Players may acquire their first Pokémon by going to Hawberry Farms. Alternately, a player may have a Pokémon from their backstory as their first Pokémon, provided that it follows the above starter Pokémon rules. Any Pokémon that is not a Legendary Pokémon and is in its lowest evolutionary form possible (including baby forms) are eligible choices for a starter Pokémon.
Though it is harder to do so, players can choose to forgo obtaining a starter Pokémon conventionally and acquire their first one through roleplay, such as capturing one themselves, befriending one, being given one by someone else, or buying a Pokémon. Pokémon acquired in this matter will not necessarily follow conventional starter Pokémon rules, for better or worse.