These are all the ribbons in Pokemon YOU the player can obtain. I excluded external world event ribbons and event ribbons on event Pokemon.
Also, if you want to know a ribbons location check serebii.net, Ribbons section.
Generation III Pokemon Ribbons (R/S/E/FR/LG/COL/XD)
#1-20.
Hoenn Contest Ribbons- (R/S/E)Beat and earn each of the 20 contest Ribbons.
#21. Artist Ribbon- (R/S/E)Defeat a Master Ranked Contest, artist in Lillycove City will give it to you.
#22. Effort Ribbon- (R/S/E/D/P/Pl/X/Y/OR/aS/S/M/US/UM)Max out a Pokemons EV stats to 510.
#23. Champion Ribbon- (R/S/E/FR/LG)Defeat the champion in R/S/E/FR/LG.
#24.Winning Ribbon- (R/S/E)Pokemon must be level 50 or under, and must have a winning streak of 56 times in the Battle Tower.
- Banned Pokemon: Mewtwo, Mew, Lugia, Ho-Oh, Celebi, Kyogre, Groudon, Rayquaza, Jirachi, Deoxys, Egg#25. Victory Ribbon- (R/S/E)Select OPEN LEVEL, and have a winning streak of 56 times in the Battle Tower.
- Banned Pokemon: Mewtwo, Mew, Lugia, Ho-Oh, Celebi, Kyogre, Groudon, Rayquaza, Jirachi, Deoxys, Egg#26. Earth Ribbon- (Colosseum, XD)Defeat 100 Pokemon Trainers in a row on MT. Battle. (You can’t switch out Pokemon on team.)
#27. Nation Ribbon- (Colosseum, XD)Purify a Shadow Pokemon. (This is kind of an event ribbon only, because only shadow Pokémon can have it.)
Generation IV Pokemon Ribbons (D/P/Pl/HG/SS)
#28- 47.
Sinnoh Contest Ribbons- (D/P/Pl)Beat and earn each of the 20 contest Ribbons.
#48-54. Daily Ribbons (D/P/Pl/HG/SS/X/Y/OR/aS)Given away on different days. Monday- Alert, Tuesday- Shock, Wednesday- Downcast, Thursday- Careless, Friday- Relax, Saturday- Snooze, Sunday- Smile.
#55. Sinnoh Champion- (D/P/Pl)Beat Sinnoh Champion Cynthia.
#56. Legend Ribbon- (HG/SS)Defeat Red on MT. Silver.
#57. Gorgeous Ribbon- (D/P/Pl/OR/aS)
#58. Royal Ribbon- (D/P/Pl/OR/aS)
#59. Gorgeous Royal Ribbon- (D/P/Pl/OR/aS)You buy ribbons #52-54 for lots of money.
#60. Footprint Ribbon- (D/P/Pl/X/Y/OR/aS/S/M/US/UM)Max out friendship with Pokemon, in gen 6 and up you have to level up a Pokemon 30 levels. (So, if you catch or transfer a Pokemon at level 71, they can't get this ribbon in gen 6 and up.)
#61. Ability Ribbon- (Pl/HG/SS)Win 21 battles in a row and defeat Palmer.
#62. Great Ability Ribbon- (Pl/HG/SS)Win 49 battles in a row and defeat Palmer.
#63. Double Ability Ribbon- (Pl/HG/SS)Get a 50 win streak in Double Battle mode.
#64. Multi Ability Ribbon- (Pl/HG/SS)Get a 50 win streak in Multi Battle Mode. (Need a friend with a DS and game)
#65. Pair Ability Ribbon- (Pl/HG/SS)Link Multi challenge mode.
#66. World Ability Ribbon- (Pl/HG/SS)Get to rank 5, on wi-fi mode. (Ribbon is no longer available, unless you use AltWFC.)
Generation VI Pokemon Ribbons (X/Y/OR/aS)
#67-71. NEO Hoenn Contest Ribbons- (OR/aS)Beat one master rank contest in selected category.
#72.Contest Star Ribbon- (OR/aS)Beat all master ranked contest.
#73. NEO Hoenn Champion Ribbon- (OR/aS)Defeat Steven Stone in OR/aS.
#74. Kalos Champion Ribbon- (X/Y)Defeat the Diantha in X/Y.
#75. Best Friends Ribbon- (X/Y/OR/aS/S/M)Max out friendship in Pokemon Amie.
#
76. Training Ribbon- (X/Y/OR/aS)Get all 30 metals in Super Training.
#77. Skilful Battler Ribbon- (X/Y/OR/aS)Win 25 times in a row in battle Maison.
#78. Expert Battler Ribbon- (X/Y/OR/aS)Win 50 times in a row in battle Maison.
#79. Contest Memory- (X/Y/OR/aS/S/M/US/UM)Have 39 or less old Hoenn and Sinnoh Contest Ribbons.
#80. Battle Memory- (X/Y/OR/aS/S/M/US/UM)Have 7 or less old Hoenn and Sinnoh Battle Ribbons.
#81. (Star) Contest Memory- (X/Y/OR/aS/S/M/US/UM)Need to have all old 40 Hoenn and Sinnoh contest Ribbons.
#82.(Star) Battle Memory- (X/Y/OR/aS/S/M/US/UM)Needs to have all 8 Battle ribbons. 2 from Hoenn and 6 from Sinnoh.
Generation VII Pokemon Ribbons (S/M/US/UM)
#83. Alola Champion Ribbon- (S/M/US/UM)Defend your Alola Champion Title.
#84. Battle Royal Master Ribbon- (S/M/US/UM)Win a Master round of Battle Royal.
#85. Battle Tree Great Ribbon- (S/M/US/UM)Have a 20-battle win streak.
#86. Battle Tree Master Ribbon- (S/M/US/UM)Have a 50-battle win streak.
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Credit
Icons where downloaded from serebii.net.