I would also suggest cutting fly-by attack out. Flying creatures are already a problem for low level characters. Minionized Shadow Bats might be good for a 3rd level party, but not for a first level party.
Party composition will also be a factor. For a party of Leaders and Strikers, the encounter could be deadly. For a party of Defenders and Controllers, it would be more managable. For a balanced party, it would still be a difficult encounter, but they would be able to get through it spending an action point or two, and maybe a daily or two.
Party composition will also be a factor. For a party of Leaders and Strikers, the encounter could be deadly. For a party of Defenders and Controllers, it would be more managable. For a balanced party, it would still be a difficult encounter, but they would be able to get through it spending an action point or two, and maybe a daily or two.