I don't like breaking theme of the Combat dice. Black shields are often used to represent bad effects for the hero when attacking, such as a monster with a Shield: Each Black Shield the hero rolls in attack, negates a Skull/Hit. Damage: Discard an equipped weapon when rolling Black Shields equal to it's power.
Good Assassin skills.
Equipped daggers thrown for free, not an action. To start that's 1 attack for free until purchasing another dagger, which would make 2. In the armoury have a Bandolier: daggers equipped off hand, max 4. Now that's quite a few 1Cd6 attacks in 1 turn for the Assassin. Giving the character some progression through purchases, the standard HQ way.
There's also a Hidden Blade, Back Stab mod we've been working on. It links with a Sneak skill.
If you want to give the Assassin speed: Roll 2d8 or roll 3d6 pick 2.
Can continue moving after you attack if you still have movement left
Most refer to this as Move Action Move or Move Attack Move, it's featured in my Character Creation here. Quite a popular skill. Works great for goblins too.
Have a look at these house rules