Rakdos, Lord of Riots here is kinda useless since most of your mana costs are B/R not colorless, it's still a good fat creature.
First of all you are playing 28 creatures which is enough, so swap those key runes for +2 Blood Crypt and -1/-2 Rakdos Guildgate since they enter tapped and they slow your aggro.That leaves you with 2 slots free, put +2 Ash Zealot . Why? Regardless if you are using it's passive it's still a 2/2 first strike with haste for 2 mana.
Also -2 Archwing Dragon and -1 Rakdos, Lord of Riots (or if you really want to play it take out a Vampire Nighthawk ) and put +3 Stromkirk Noble . It's a 1 mana drop 1/1 who can get bigger if the oponent started with soldiers to chump block and stuff. Archwing dragon is not bad but remember that in an aggro deck your main drops should be 1,2 and 3 mana creatures and spells.