Board Thread:General Discussion/@comment-25926288-20170429134340/@comment-25375217-20170501032002

I suspect most of Black's power came from her time in the Dark Realm (though, of course, we'll never be told that canonically). It's stated to be a place of great dark power, so I'd say sometime between 619 and 609, she took advantage of its inherent darkness to master dark magic and become the dark magic-resistant powerhouse who can break out of squid ink and walk through Zelena's magic.

So my ranking would be:
 * 1) Deities
 * 2) Zeus, Kronos, Hades with his heart - life-granting stuff
 * 3) Hades without his heart
 * 4) Morpheus, Hephaestus, Cupid - deities with a specific duty
 * 5) Ursula, Nyx - lesser deity
 * 6) Deified Humans Part A
 * 7) Merlin - light magic deification
 * 8) Nimue, Enhanced Mr. Gold - enhanced dark magic deification
 * 9) Dark Swan - dark magic deification plus inherent light magic
 * 10) Believers
 * 11) The Dragon - enhanced belief
 * 12) Henry - spotty belief but powerful when it works
 * 13) Deified Humans Part B
 * 14) The Apprentice - trained by deified human in enhanced light magic
 * 15) Dark Hook, Zoso, Gorgon, Rumplestiltskin Classic - basic dark magic deification
 * 16) Fairies
 * 17) Black Fairy - fairy magic, extreme magic knowledge, and enhanced dark magic
 * 18) Reul Ghorm - fairy magic and enhanced light magic
 * 19) Fairy Godmother, Tiger Lily - fairy godmothers
 * 20) Nova, Tinker Bell, Silvermist, other fairies - fairy magic
 * 21) Inherent Magicians
 * 22) Emma Swan, Aladdin, Unedited Rumplestiltskin - inherent Savior magic
 * 23) Zelena - inherent dark magic, broke a law of magic
 * 24) Glinda - inherent light magic (presumably?)
 * 25) Ingrid - basic dark magic and inherent elemental magic
 * 26) *Mombi, Nessarose - inherent magic (presumably), unknown light or dark
 * 27) Trained Magicians
 * 28) Enhanced Jafar - no laws of magic
 * 29) Maleficent - enhanced dark magic and dragon magic Genie Jafar - enhanced dark magic and genie magic
 * 30) Cora, Amara, Jafar Classic, DunBroch Witch - enhanced dark magic
 * 31) Ursula - basic dark magic, mermaid magic
 * 32) Peter Pan - location-based belief, basic dark magic
 * 33) Regina, Gideon, Anastasia, Trish - basic dark magic
 * 34) Genies
 * 35) Aladdin, Cyrus, Sidney, Rafi, Taj, Will - genie magic
 * 36) Mermaids
 * 37) Ariel, other mermaids - mermaid magic
 * 38) Elsa - inherent elemental magic
 * 39) Lilly - dragon magic
 * 40) Grand Pabbie - rock troll magic
 * 41) Cruella de Vil - persuasion

I left out Jabberwocky because I believe she doesn't really have magic, she's just good at reading people. If it is magic, she'd probably be somewhere around Lilly. I think I included just about everyone else, though...?