Hextech chests and rerolls pull from the loot pool: 1,721 skins right now. Most are Common store skins, but 508 of them aren't in the regular store. Those are the pulls worth getting excited about, and the shards worth unlocking rather than disenchanting.
The best pulls, scarcest first
Skins you can still get from loot, sorted by rarity, then by popularity:
Divine God-King DariusDarius · 1% drop rate from event capsules or the SanctumVery rare
Fallen God-King GarenGaren · 1% drop rate from event capsules or the SanctumVery rare
Genesis Nightbringer YasuoYasuo · 1% drop rate from event capsules or the SanctumVery rare
Admiral Battle Bunny Miss FortuneMiss Fortune · 1% drop rate from event capsules or the SanctumVery rare
Dark Cosmic Erasure JhinJhin · 1% drop rate from event capsules or the SanctumVery rare
Hextech AnnieAnnie · 125 Mythic Essence, only while it's in the rotating Mythic shopRare
Dreadnova DariusDarius · 125 Mythic Essence, only while it's in the rotating Mythic shopRare
Lancer Zero HecarimHecarim · 125 Mythic Essence, only while it's in the rotating Mythic shopRare
Ashen Knight PykePyke · 125 Mythic Essence, only while it's in the rotating Mythic shopRare
Soulstealer VayneVayne · 125 Mythic Essence, only while it's in the rotating Mythic shopRare
Dark Star Cho'GathCho'Gath · 125 Mythic Essence, only while it's in the rotating Mythic shopRare
Prestige True Damage SennaSenna · 150 Mythic Essence, only while it's in the rotating Mythic shopRare
Hextech Kog'MawKog'Maw · 125 Mythic Essence, only while it's in the rotating Mythic shopRare
Prestige True Damage QiyanaQiyana · 150 Mythic Essence, only while it's in the rotating Mythic shopRare
Prestige K/DA Kai'SaKai'Sa · 150 Mythic Essence, only while it's in the rotating Mythic shopRare
Prestige True Damage YasuoYasuo · 150 Mythic Essence, only while it's in the rotating Mythic shopRare
Prestige K/DA AkaliAkali · 150 Mythic Essence, only while it's in the rotating Mythic shopRare
Hextech SwainSwain · 125 Mythic Essence, only while it's in the rotating Mythic shopRare
Hextech RenektonRenekton · 125 Mythic Essence, only while it's in the rotating Mythic shopRare
Prestige Battle Academia LuxLux · 150 Mythic Essence, only while it's in the rotating Mythic shopRare
Hextech AlistarAlistar · 125 Mythic Essence, only while it's in the rotating Mythic shopRare
Prestige K/DA AhriAhri · 150 Mythic Essence, only while it's in the rotating Mythic shopRare
Hextech MalzaharMalzahar · 125 Mythic Essence, only while it's in the rotating Mythic shopRare
Prestige PROJECT: ZedZed · 150 Mythic Essence, only while it's in the rotating Mythic shopRare
Prestige Nightbringer KaynKayn · 150 Mythic Essence, only while it's in the rotating Mythic shopRare
Hextech RammusRammus · 125 Mythic Essence, only while it's in the rotating Mythic shopRare
Hextech PoppyPoppy · 125 Mythic Essence, only while it's in the rotating Mythic shopRare
Ashen Graveknight MordekaiserMordekaiser · 125 Mythic Essence, only while it's in the rotating Mythic shopRare
Prestige Obsidian Dragon SettSett · 150 Mythic Essence, only while it's in the rotating Mythic shopRare
Prestige K/DA ALL OUT Kai'SaKai'Sa · 150 Mythic Essence, only while it's in the rotating Mythic shopRare
What to do when you pull one
If it's a champion you play, unlock it: you can't just buy a non-store skin later. The Orange Essence cost for each price tier is in reroll, disenchant or unlock, and each skin's page shows its own numbers.
Want the full picture, including skins you can't get from loot at all? See the rarest skins in League.