in short like motorcycle item can buy. but it be pokemon doesnt need to be animated like a aerodactyl, rapidash, charizard, rhydon, etc as examples.
then for surf mount cosmetic would change the base surf appearance when used to a dragonair, blastoise, gyarados,etc.
special event ones could be legendary like a lugia, ho-oh, groundon, zapdos,etc for land. kyogre, lapras, rare water pokes,etc as the water cosmetic. that can earn either through pvp or pve tokens, out right buyable for reward points, etc.
i the surf ones just serving as skins more or less to go over the regular surf mount image for the games. idk if its possible in pokemmo. just what iv seen in other games that player base loved, and was good source of income that was purely cosmetic.