but I don't see it being that bad
And that's the problem, it isn't that bad......only thing is that Scarecone isn't that good either. It does absolutely NOTHING by itself(cycling for 4 mana is nothing imo, no critters in GY? Still nothing), and isn't even a decent beater for 3 mana. It's one of those cards that a deck would have to be almost completely built around it for it to achieve mediocrity.
Also, lets examine if you get that 2nd Crone:
Cast him(3 mana)
He's useless, trade him for a card(1 mana)
Bring him back(4 mana)
Sack him again to finally gain card advantage(1 mana)
So that's 9 mana total to see 2 new cards, but doing so only increases your hand size by 1. I know for a fact that MUD decks can do sooo much better with the allocation of 9 mana.
The only 'snowballs chance in hell' Scarecrone really has is in a MUD aggro build. To actually get a benefit you would need to 'cheat' fat creatures into play by somehow getting them into the yard via Bazaar or some combination of Masticores/Razormanes. I don't think there is a much better aggressive creature than Sundering Titan. But this of course leads back to my point that the deck would have to be built around Crone. Having 2 uncastable fatties in your hand is bad.
I think Umbral Mantle is another card that falls in the 'not that bad' category because in all honesty a turn 1 Metalworker has the potential to swing for lethal dmg on turn 2. Staff is still a better card. Both Mantle and Staff are
essentially Metalworker equipment if you really look at it.
Mike
p.s. don't let any of that stop you from testing the card out though.