Hm.
Contains sixteen in the Lylat System: Corneria, Venom, Sauria, Titania, Fichina, Fortuna, Katina, Macbeth, Solar, Zoness, Aquas, "Secret Base", Eladard, Papetoon, Aparoid Homeworld, and Grippia.
Looks like fifty-three in a Metroid wiki. (Shows 60 items. Excluded categories and such.)
Displays only galaxies in Mario's universe. Will blindly estimate four per galaxy. Stuffed 91 galaxies into these games.
Found 35 for Kirby's universe, 25 across Tales games, 9 in Fire Emblem, 47 for Final Fantasy, Weyard from Golden Sun, 69 in the Marvel universe, 153 or so in DC's universe, and Planet of the Apes.
Totals 773 planets. Forgot Starcraft's ~180 and Warcraft's ...unclear number. Will just say 17. Oof, and Star Wars and Star Trek. Tacks on 924 and maybe 950, respectively. Balloons to 2844 planets total.
(Uh, Google? Asked "Legend of Zelda Worlds" without quotes. Why is "How do Gorons have babies?" one of the question searches?)
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Do you do anything special on your birthday?