Alcremie has the most possible forms among Pokémon when Mega Evolutions and gender differences are excluded.
Its 63 standard forms come from combining nine cream colors with seven decorative Sweet items, such as Strawberry, Berry, Love, Star, Clover, Flower, and Ribbon Sweets. Alcremie evolves from Milcery, and the result depends on the Sweet held and how the player spins the character.
The evolution method also considers the direction and duration of the spin, as well as the time of day. That is why Alcremie is not simply a Pokémon with seven cosmetic variants. Its combinations produce a much larger total than familiar form-changing Pokémon.
Unown has 28 letter and punctuation forms, while Vivillon has regional wing patterns. Those are common alternatives, but neither reaches Alcremie's total. Alcremie also has a Gigantamax form, although the question's exclusion concerns Mega Evolutions, not Gigantamax.