Ooh, Dimir Cutpurse as it always wanted to be :) This is a very Time Spiralesque mashup of Dimir Infiltrator and Dimir Cutpurse. Good card, but pretty fair for its cost.

Cool card. But it should be uncommon, I think.

Whoa, you reckon? That's a pretty spicy pair of abilities.

­Scroll Thiefs are common. Specters are often rare because they put more awesome abilities (and, okay, Hippie still is), but the most straightforward can be uncommon (even when they all fly and everything). Since you only do one of the two, its awesomeness is capped.

Or maybe the Dimir want me to underestimate it. o.O

I don't think an unblockable Scroll Thief would be common. In fact, there have only ever been three creatures with both unblockable and a saboteur ability. Ferropede was uncommon, but had a much more minor effect; the other two - Ghastlord of Fugue and Higure, the Still Wind - were rare. In fact, this is quite like a smaller Ghastlord of Fugue with an alternate option too.

There's also "Giving an archtype exactly what they want = Rare" argument, which I could dig. I'm pretty sure there are some players who would love to have this card. Those players would treat the card as special, and rareness denotes specialness.

Oh, and I suppose there's the precedent argument. Specters with evasion are almost always rare. You could make this uncommon, sure. But then future specters with evasion could now be uncommon. The next time you print a new riff on Hypnotic Specter, if it wasn't uber-powerful, players would complain that it should have been uncommon. I don't know how much I follow this logic, but it seems like a valid argument.

Personally, I think the card could be either uncommon or rare, depending on how many 'must-be-rares' end up in the set. I'd probably promote this as an uncommon that with the hashtag "Most likely to become rare when something falls out of the file."