I've scoured the internet for a bass tab for this song and turned up empty 
handed...so I thought I'd give tabbing the song out a shot! 
This is a drop D alternative for the song, as I'm pretty sure My Darkest Days play in drop C.
It's kinda hard to look at I know, but I'm 100% sure that all of it is right. 
Anyways, happy rocking! (-:  

Intro: (Come in at 0:17)
Play along to the bass drum and snare and listen carefully.   
g|---------------------------|
d|---------------------------|
a|---------------------------|
D|-8-88-86-66-64-44-466666-6-| x2
Verse 1: (11's, not 1's)

g|-----------------------------------------------------------------|
d|-----------------------------------------------------------------|
a|-----------------------------------------------------------------|
D|-8-/11-8-6-/11-8-4-/11-4-6-/11-6-8-/11-8-6-/11-8-4-/11-4-6-/11-6-| x2

Chorus 1: (Same as Intro x4)

Bass fill after Chorus 1: (Come in at 1:13)

g|----------------|
d|-868686-6868686-|
a|----------------|
D|----------------|

Verse 2: (Same as Verse 1 x3)

Chorus 2: (Same as Intro x4)

Bass fill after Chorus 2: (Come in at 2:04)

g|--------56856-5--------6--------------|
d|-8686868-----8--86-6810-1086----------|
a|------------------9---------888888888-|
D|--------------------------------------|

Chorus 3: (Same as Intro x4)

Outro:

g|--------------------|
d|--------------------|
a|--------------------|
D|-88888~-88888~-8-8\-|

Any questions, feel free to ask me at willgenius@live.co.uk! Peace out guys! (-: