So does this let you cast it at any time or does this let you pay towards casting it by paying portions of it's mana cost (at any time)?

The former seems regular, the latter seems weird but pretty flavorful and awesome.

I think the intent is that you can spend the mana over time to pay it back. I have no idea how you'd actually implement that though - why would I not just drop a handful of cards with these at the very start of the game, and promise to pay for them on turn 16?

no, Froggy’s second thought is correct. You could exile this on turn one and pay , then pay on turn two to cast it from exile.

See Mega Mech

Oh. Well, that's kinda ok-ish; like storage lands for specific spells. Though this is a pretty bad example for it. I mean, "Whee, I can drop a 2/2 on turn 2 if I skip my one-drop" is not very exciting.

Well it is just a common. I was going to say "Well it is strictly better than..." But after looking through common artifact creatures with cmc 3, the only options are Stonework Puma, which is an Ally, and Sliver Construct, which is a Sliver.

I mean, it's not awful. I think it's about right for a common. I wanted one small Manufacture creature as a late pick. The rest are going to be much larger.

There are lots of examples of cards of a similar power level. I thought about upping this to 2/3, but I actually haven't seen a 2/3 for without some kind of drawback at common.

There. Now it's strictly better than Gilded Sentinel, and cost is high enough that manufacture is interesting.

That's pretty neat.