Its been a bit, so here is a longer entry for DnD Next how about a new speciality one only for rogues who want more fun for sneak attack.
Other may focus on helping their friends, some focus on feats of strengh, and a few focus on understanding the world. You just want to see things die. No murcy, no quarter, just death.
Death Dealers arize from several area, all of them ussaly with sad backrounds. Beaten, starved, or born mean, no one things makes a death dealer. They how and why are not important. All that matters is something in in your way and you will end it.
Level 1: Sneak Attack Basics
Level 3: Sneak Attack Intermediate
Level 6:Sneak Attack Journeyman
Level 9:Sneak Attack Master
Sneak Attack Basics
You train yourself to hit your target hard
Prerequisite: 1d6 sneak attack
Benefit: When you attack with sneak attack and roll its damage dice, roll an extra die of the same type, drop the lowest roll, and then add up the damage.
Sneak Attack Intermediate
Your continued training really begins to cripple your targets.
Prerequisite: Sneak Attack Basics
Benefit: When you attack with sneak attack and roll its damage dice, roll an extra two dice of the same type for up to two dice, drop the lowest two rolls, and then add up the damage. In addition, you gain a +1 bonus to attack rolls that when you perform a sneak attack.
Sneak Attack Journeyman
You have almost perfected the technique of crippling your enemies from the shadows.
Prerequisite: Sneak Attack Intermediate
Benefit: When you attack with sneak attack and roll its damage dice, roll an extra three dice of the same type, drop the lowest three rolls, and then add up the damage. In addition, any enemy hit with a sneak attack now takes a -1 penalty to all d20 rolls until they make a constitution save equal to 10+your dex modifier at the end of your turn.
Sneak Attack Master
You are death incarnate.
Prerequisite: Sneak Attack Journeyman
Benefit: When you use Sneak Attack Journeyman, you may now roll two more extra dice and use the highest of these dice up to the number of dice you are allowed by your sneak attack class feature. You may take the feat more then once. Each time you do, you gain the benefit of rolling two more sneak attack dice.