THE BLACK GOBBO

With ASF and I5 he potentially is putting out 5 attacks almost always getting rerolls to hit, Str4, and -4 save modifier. Even from the front it's 3 attacks.
He lacks the poison some other assassins have but it seems pretty killy. Maybe a little too killy? Is the skewerers rule too powerful?

---------I see it like this: his profile is a standard Goblin Big Boss with  +1 WS and +2I. He is normally going to have 4 Attacks (standard Nasty Skulker have 3A in total, btw), and only gets 5 on the flank or 6 in the rear. These bonus attacks are situational and make the Goblin player exercise a degree of tactics.

Although the save modifier is high (i.e. -4), it is also situational because it's only good against heavily armored targets. Though I could see dropping it to -3 or removing the armour penalty from the weapon altogether (so he would have only a -2 armour save modifier). Perhaps -4 armour save is a bit much?

But also remember he is kinda squishy. With only a T4 and W2 with light armour, he can be killed in combat rather easily and quickly. The 5+ ward might keep him in the game a bit longer. In a typical combat he probably won't be attacking more than twice before he's killed, especially if the enemy is trying to get rid of him.

I modified the Sneaky Skewerers to only a -1 armour save, so in total it's -3.

So Black Gobbo potentially has better damage output against higher armor save troops, but relatively worse output against higher toughness troops (poison) the other assassins have more flexibility with throwing weapons once revealed. Black Gobbo has Str and T compared to them but otehrwise worse ward save.

You are right it's pretty darn comparable.

I still can't find his left arm.
Makes it more difficult to fight him!