As nobody has tabbed this song yet. I thought that I should tab it out. 
I did learn how to play this song by watching someone playing it on YouTube.
But some of the things sounded wrong. This is how I learnt how to play it.

Song - Nightmare
Artist - Eleventyseven
Tabbed - Mattdude92
Tuning - Drop D (DADGBe)

h - Hammer-on
p - Pull-off
/ - Slide up


Intro - First Part
e|-------------------------------|
B|-------------------------------|
G|-44------------66--------3p1---|
D|-44-3h4-44-3h4-66-4h6-11-----4-| (1s Not 11s)
A|-22-----44-----44-----11-------|
D|--------44------------11-------|

e|---------------------------|
B|---------------------------|
G|-44------------66-----66-3-|
D|-44-3h4-44-3h4-66-4h6-66-3-|
A|-22-----44-----44-----44-1-| 
D|--------44-----------------|

Second Part
e|-------------------------------|
B|-------------------------------|
G|-44------------66--------------|
D|-44-3h4-44-3h4-66-4h6-11-3p1---| (1s Not 11s)
A|-22-----44-----44-----11-----4-|
D|--------44------------11-------|

e|-----------------------------|
B|-----------------------------|
G|-44------------66-----66-----|
D|-44-3h4-44-3h4-66-4h6-66-4h6-|
A|-22-----44-----44-----44-----| 
D|--------44-------------------|

e|----------------|
B|----------------|
G|-4-6-8-9-111111-|
D|-4-6-8-9-111111-| (11s NOT 1s)
A|-2-4-6-7-9 9 9--|
D|----------------|

Verse
Work out timing for yourself for this bit.
e|------------------------------|
B|------------------------------|
G|-44-66-----------44-6---------|
D|-44-66-44444-11--44-6-44-4-11-| (1s Not 11s)
A|-22-44-44444-11--22-4-44-4-11-| Played twice
D|-------44444-11-------44-4-11-|

Pre-Chorus
e|-------------|
B|-------------|
G|-4~----3~----|
D|-4~-4~-3~-1~-| Played Twice
A|-2~-4~-1~-1~-| (Im not sure if it's multi-strum second time round.
D|----4~----1~-|         Try it yourself see what sounds best)

e|-------------------|
B|-------------------|
G|-44444444-66666666-|
D|-44444444-66666666-|
A|-22222222-44444444-|
D|-------------------|
PM ........ ........

Chorus
e|-------------|
B|-------------|
G|-------------|
D|-44-66-99-99-| Play twice
A|-44-66-99-99-|
D|-44-66-99-99-|

e|---------------------------------------------|
B|---------------------------------------------|
G|---------------------------------------------|
D|-44444444-66666666-99999999-1212121212121212-|
A|-44444444-66666666-99999999-1212121212121212-|
D|-44444444-66666666-99999999-1212121212121212-|

e|-------------|
B|-------------|
G|-------------|
D|-99999999-12-|
A|-99999999-12-|
D|-99999999-12-|


Play the second part of the intro once.
Verse
Pre-chorus
Chorus

Bridge/Middle 8
This bit was a bit tricky to figure out but easy to play.

e|---------|                   e|---------|
B|---------|                   B|---------|
G|---------|                   G|---------|
D|-8-4-6-4-| On 4th time play  D|-8-4-6/8-|
A|---------|                   A|---------|
D|---------|                   D|---------|

Lyrics kick in

e|---------|                   e|-----------|
B|---------|                   B|-----------|
G|---------|                   G|-----------|
D|-8-4-6-4-| On 4th time play  D|-8-4-6/8-4-|
A|---------|                   A|-----------|
D|---------|                   D|-----------|

I dont know this next bit. You can figure it out on your own sorry.

Back into chorus then end.

Structure 
- Intro
- Verse
- Pre-chorus
- Chorus
- Intro
- Verse
- Pre-Chorus
- Chorus
- Middle 8/Bridge
- Chorus -End

Thats the song done, you will have to work bits of the timing yourself
I gave you the basic chords. If you have any comments about this tab
or if some things are wrong please Comment and rate. :)
Enjoy and keep rocking \m/