Azazel

It was late evening. It had long since fallen dark outside, and rain was lazily beating against the apartment windows. The room was lit only by the dim light of a few candles. Scattered around were cans of paint, a smartphone on a tripod, an open laptop with tabs on ancient rituals, and mugs of long-cold coffee.
— So, are you ready? This video is definitely going to fly.
You chuckled, picked up some red paint, and began drawing a huge magic circle right on the floor. Inside it appeared strange symbols, stars, runes, and long Latin phrases you'd found on some shady forum. The whole thing seemed like a silly stunt for the sake of content.
— Imagine if someone actually came now...
You both laughed.
The phone was already recording.

• Three... two.. one..
  You spoke Latin words loudly.
  Nothing.
  Second.
  Two.
• What nonsense..
  But suddenly...
  Click.
  The lights started to flash.
  Click. Click. Click.
  The air suddenly became heavier. The temperature in the room dropped so much that steam began to come out of my breath.
• You... did this on purpose?
  Didn't have time to finish.
  BAM!
  The light disappeared completely.
  Absolute darkness fell.
  All that could be heard was my own breathing and a strange low hum, as if something huge was moving somewhere under the floor.
  After a few seconds the lights came on again...
  But no longer white.
  They glowed a deep blood-red color.
  The room seemed to be filled with scarlet light.
  The circle on the floor flared brighter than hot metal.
  The drawn words began... to move.
  The letters were lifted off the floor, swirled around, changed places, and formed completely new sentences in an unknown Latin.
  The candles went out simultaneously.
  A thick black fog rose.
  It slowly flowed out from the center of the circle.
  The walls shook.
  There was a low, muffled roar that made everything inside me clench.
  A huge clawed hand appeared from the fog first.
  Then long black hair with white streaks appeared. Massive, curved horns slowly emerged from the darkness.
  A tall figure stepped forward.
  His skin was pale as marble, and dark patterns ran across his powerful body.
• Who dared?...