I don't think it's worth it to make it multi-colored.

My original take on the flavor was that the Disassembly-Worker takes apart its fellow Assembly-Workers out of its own greed and selfishness, in which case the Disassembly-Worker would just be 2B with a B activation. I also intentionally permit it to target your own Assembly-Workers to go along with this theme. If I make it an activation for R, it just becomes an act of passion. Which still works since I was going for an Assembly-Worker that's gone rogue, but doesn't fit as well with the idea of greed/selfishness.

The B activation is supposed to read more like a "destroy" effect, just templated as a fight for flavor.

Could this be black with a red activated ability? I don't know the exact restrictions of the challenge by heart.

Yeah, kicker would definitely work for this, I was just avoiding keywords in general. I could also consider Replicate.

The name was originally just Obstruct, but I wasn't sure if people would read it as an order/command, and Commands already have that namespace taken up.

The additional cost is at the beginning because that's typically where additional costs go, and the copy ability is at the end because that's typically where spells that copy themselves copy themselves. I could remove the additional cost and template it like the Chain cycle, and either add a mana cost to copy or change it so you only get one tap.

Wow this is wordy for a small effect.

Would 'kicker' actually shorten it?

Tap target creature.
Kicker (tap an assembly worker you control): Tap another target creature.

If you want to restrict it to creatures and disallow noncreature permanents (and tribal ones with changeling only exist in custom cards) to tap for this you'll need to add "creature" - otherwise you're fine.

It's really a bad idea to add a colon to a card name since now every mention of the card name makes it look like you have an activated ability. Magic-players are specifically trained to make that connection.

The ability seems like a good keyword candidate, but on this card it looks just too wordy for a marginal effect.

I'm aware you aren't allowed to make upa new keyword for the challenge, but that makes this effect a suboptimal choice for the parameters given.

I don't see why the copy effect is so far separated from the additional cost. This isn't kicker, you don't have to keep the cost entirely separate because it's a keyword on its own.

This is basically tribal one-creature conspire. Putting the cost and effect closer together like in that reminder text seems preferable to make it clear what goes on and makes it easier to tell what happens if you eshew the additional cost; only one line will be left: "Tap target creature." and it can its own paragraph.