Mascot Legends: Solgaleo, Lunala.
Tapu Legends: Tapu Koko, Tapu Fini, Tapu Bulu, Tapu Lele.
Ultra Beasts: Nihilego, Buzzwole, Phermosa, Xurikitree, Kartana, Celesteela, Guzzlord.
Other: Necrozma, Magearna.
There's also Marshadow, but I'm pretty sure that it's more of a mythical Pokemon than a legendary, plus you can't even find it in-game.
Note: I'm not 100% sure if the UB's are counted as "Legendary Pokemon" but I'm putting them on this list because they seem to be similar to most legendaries.