A lot of Pokémon don't show up in that list, but they do exist in the database. (Example: Skiploom.) You can access Marill's page
here. It's because Pokémon in the
NFE tier aren't included in those lists by default. You can change this preference
here by setting the Tier Threshold to NFE, but keep in mind your settings may not stay permanently. There appears to be a
problem with this presently, but hopefully this will solve your problem.