The idea here is basically a bunch of stuff that damages your opponent upon its death topped off with Torbran and Jaya to deal extra damage, Judith to ping them again and trigger Torbran and Jaya again. Fireblade Artist, Angrath's Rampage, Ayara, and Witch's Oven to get a sacrifice when you need that extra bit of damage from Mayhem Devil (who then triggers Jaya and Torbran again and possibly Judith if it was a nontoken). Rankle and Clackbridge Troll are late additions that I just wanted to test out for the additional sacrifices to fuel Mayhem Devil further...funny that a devil deck includes a way of giving your opponent goats to sacrifice.  All the tiny token creatures will trigger Cavalcade of Calamity as long as Judith is not on the board, then Cavalcade triggers Jaya and Torbran. Jaya's Greeting for a more targeted kill. In the most perfect setup, you can drop Massacre Girl to kill off all the cheap devils at once and trigger all the extra damage from Torbran, Jaya, and Judith...it stacks very fast because Judith's extra damage is from her and not from the dead creature so she triggers Jaya and Torbran again which makes each Footlight Fiend or Tibalt's Rager worth a potential 8 damage upon its death if you have the whole setup on the board. She does not trigger off tokens, so each of Tibalt's devil tokens is only doing 4.  Also, don't forget about Ayara's black creature trigger and the Cauldron Familiars, cheap ETB triggers are a nice addition here; then toss those cats in the Oven for a bit more damage...oops, the cat was sacrificed, trigger Mayhem Devil and Judith, trigger Jaya and Torbran...yeah...that one cat can do a lot of damage when set up properly...and then bring it back by sacrificing the Food token the Oven made...and repeat with the other Oven when possible.

The deck is literal mayhem! Plays exactly how I would expect a Rakdos festival to play! Lots of death, lots of wanting your own stuff to die, lots of craziness. 

Some other interesting bits I was looking at were Ember Hauler and Mask of Immolation, I just like devils more than goblins and attacking more than sacrificing. Although Goblin Bombardment would be a nice add. I may get Zariel just for the once per turn free explodey devil power.

Also,  I'm too lazy and too casual of a player to make a sideboard.

Sorry, I like to babble...TL;DR...attack with explodey devils and/or sacrifice them so they damage your opponent when they die. Devils dealing damage and/or dying trigger something for additional damage.