Top 10 Extreme Metal Songs Featuring Keyboard InstrumentsAll instruments using a keyboard are allowed - piano, organ, accordion, electronic keyboards, including synthesizers and digital pianos.
If you think that using keyboard instruments in extreme metal is weird, you are probably right because it isn't typical but it exists.
Keyboard instruments are mainly used in progressive metal, symphonic and power metal but in general, these instruments aren't typical in metal music - most of the metal bands don't use them on a regular basis.
However, metal music has been becoming more and more progressive over time and this trend includes more often utilization of keyboard instruments because these instruments setup a "progressive" sound.
Here are some examples - there are even technical death metal songs with piano.
The Top Ten
This is a very heavy song (technical death metal) with a long, soft and beautiful piano intro (30 secs long).
Phobophile is probably the most acclaimed Cryptopsy song. Is piano partly responsible for that? - Metal_Treasure
It's technical death metal - this band uses real piano and uses it often - Metal_Treasure
Melodic death metal with keyboards - Metal_Treasure
Technical death metal with a piano intro for 40 secs. - Metal_Treasure
They used a real piano in the short piano intro and later in the song (the band plays melodic death metal). - Metal_Treasure
Black metal from Austria. - Metal_Treasure
Black metal from Switzerland. - Metal_Treasure
Real piano throughout but around 4:20 you can hear it better. - Metal_Treasure
This is probably a xylophone. - Metal_Treasure
Again, it's a real piano - Metal_Treasure