Pokémon as a franchise hasn’t changed up its core mechanics much over the years, but Pokémon Legends: Arceus took steps to make even the most basic features look at least somewhat different.
Prior to this game, evolving a Pokémon would involve getting the species to a set level and just watching an animation. Legends: Arceus has turned it into something players need to do manually from their satchel, making it so you can keep a Pokémon unevolved as long as you want without needing to constantly cancel animations.
When viewing your Pokémon from the satchel, the new Evolve option will be selectable if you have reached the requirements to evolve that species into its next stage.
Trade Evolutions/Held Items
Legends: Arceus has maintained the use of evolution items too, such as Evolution Stones and items beloved by certain species. Because Held Items have been removed from the game, however, items that previously would have needed to be held have turned into consumables.
This is also true for Trade Evolutions, as players can now obtain a consumable item called the Linking Cord that will replace the need to connect with other players, enabling Legends: Arceus to be 100 percent completed as a solo experience.
For example, using a Reaper Cloth on Dusclops will get you a Dusknoir where you would previously need to trade a Dusclops holding the item to trigger its evolution.
Moves/Time of day
Some Pokémon like Piloswine and Bonsly will still evolve after learning a specific move and then leveling up.
Time of day will also continue to play a big role in evolving certain species of Pokémon, both when leveling them up and using items. One of the most interesting examples of features combining is present with Johtonian Sneasel and Hisuian Sneasel, which require the use of a Razor Claw to evolve.
Using the Razor Claw on Hisuian Sneasel during the day will evolve it into Sneasler, while you have to use the item on Johtonian Sneasel at night to get Weavile.