There are so many songs out there, some are bound to fit the Main Six, Princesses, side characters, villains, whatever.

Pick a character then post a Rock/Heavy Metal song that fits the character. pmv's count as well

Let me start off easy with Rainbow Dash.

Eh, I'm never very good at things like this, but this song reminds me of Derpy as she is portrayed in the fandom.

Resilience by As I Lay Dying

Lyrics

1410548
For Chrysalis

Pinkie Pie would like pop punk bands like Fall Out Boy.
Fluttershy is the biggest fucking metalhead in the world (Slayer, Iron Maiden, Opeth)
Applejack would listen to stuff like Johnny Cash.
Rarity would listen to Radiohead.
Twilight Sparkle would like Beatles and Pink Floyd.
Rainbow Dash listens to Nirvana and Mudhoney.

1414247 Have a vote-up just for the Opeth.

If it counts, I think "Owner of a Lonely Heart" by YES would fit Fluttershy quite well.

1410548 Pinkie Pie - What's my age again by BLink 182

Rainbow- Stand Up by Woe is Me

Luna- Evil Angel by Breaking Benjamin

Fluttershy- Wait and Bleed by Slipknot

Rarity- hey Mrs. Dramaqueen by Eskimo Callboy

1410548 For Luna I'd have to go with Haunted by Disturbed

the mane 6 would be this
fluttershy would be this song. cause shes a tree

pinkie for obvious party reasons

twilight is the biggest nerd rocker ever

rarity for the added fashion sense

Rainbow is obviously super into thrash

and applejack for the bluesy undertone