According to statistics from Apex Status there have been over 550 skins released for Apex Legends. Some of those skins were limited time releases that haven't resurfaced in the in-game store since their initial drop, making them incredibly rare. Keep in mind that these are the rarest skins in the game, not the objective best or necessarily even fan favorites.
5 Rarest Apex Legends Skins in the Game
5. Airship Assassin - Wraith
The Airship Assassin skin is a notoriously sought after skin for Wraith mains. The skins was available upon Apex Legends' initial launch for about a month, but was then removed from the store to make room for newer cosmetics. It has briefly reappeared in the store a couple of times since then which has made it more common, but this skin is still pretty rare.
4. Bionic Wonder - Wattson
Wattson's Bionic Wonder skin is a bit of a controversial one. It was a dramatic shift in design compared to Wattson's other skins and a good deal of players didn't care for it. The skin also hasn't been available in the store since October 2019, making it incredibly rare even for the few fans who enjoyed the design.
3. Outland Warrior - Bangalore
The Outland Warrior skin is Bangalore's rarest skin by far, as well as one of the rarest in the game. It was released during the Wild Hunt event in Season 1 but hasn't returned to the store since. Given that this is an event skin, there is a good chance this skin might never make a return.
2. Great Winter - Bloodhound
Great Winter is a recolor of Bloodhound's Imperial Warrior skin. This means to purchase this skin players will also have to have the Imperial Warrior skin unlocked. But the primary challenge with purchasing this skin is that it hasn't returned to the in-game store since March 2019. Reputable Apex Legends data miner Shrugtal on twitter has stated they expect it to be rereleased in the second half of Season 10.
1. Dark Artist - Mirage
Mirage's Dark Artist is likely the rarest in the game for the same reason as many of the skins in this list - it hasn't been available for purchase since Season 1. Players must have the Ghost Machine legendary Mirage skin to purchase Dark Artist. Shrugtal said that Dark Artist should also be available in the later half of Season 10.