I may as well start doing actual write-ups for the top 20.

20) The Legend of Zelda: A Link to the Past (SNES / 95 / 1991)

Once again, the highest Nintendo game on my list. I find that a lot of games don't really hold up anymore as you pass the tenth anniversary of their release. Case in point: 95% of PS1 games. LttP is now 22 years old and still as brilliant as ever. The top-down design means that it's still playable despite its age, and as such the brilliant level design, combat and boss battles still shine through.

I'll continue from 19 once it's been guessed.

Hints:

#16 - Edge.

#15 - A prequel that was nearly as good as the original in my opinion, although most would disagree.

16.  Cross Edge(eww,) Soul Edge, Final Fantasy 4, or Star Ocean the Last Hope?

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Answers

20.  Advertised on the box as "hard to beat."  Ninja Gaiden 2 The Dark Sword of Chaos

19.  First time you saw this character in a game, anyone else else think the male robot was a girl?  Mega Man X.  Just because of the long hair, I thought Zero was a female the first time I saw the game.  This was a long  time ago.

18.  Your allies can use magic, climb on the ceiling, or turn into a bat.  Castlevania 3.  Sypha can use magic, Grant can climb on the ceiling, and Alucard can turn into a bat.

Or Mirror's Edge, Soul Calibur (Edge Master), Rival Schools, Atelier Iris 3... it could be tons of games.

Hints

17.  You fight dark versions of eight bosses that were in the previous game. 

16.  The main character is the last boss when playing in a different mode as the games three supporting characters.

17 - Final Fantasy X-2.

I know I said most games will be RPGs afterwards but the hint for  this game isn't an RPG.  Both aren't RPGs actually.  There are eight dark bosses in FF10-2 though?  Eight exactly?

Valefor, Ifrit, Ixion, Shiva, Bahamut, Yojimbo, Anima, Dark Magus Sisters off the top of my head in Final Fantasy X (the previous game). If you don't count the multiple fights against Yojimbo and Ixion, fight the Magus Sisters separatedly, or count Penance as a dark boss... yes.

You fight their regular versions at the end of the game.

So bloody close that I'm gonna have to give this to you.  It was Oath in Felghana :)

I'm getting a bit ahead of myself, so I'm making them harder.

"Edge" has nothing to do with the title.