BF Weaknesses(from Wikia)

Blackwings have some problems maintaining Hand and Field Advantage due to the overwhelming speed with which Blackwings are summoned, a player can (and often will) find his/her hand depleting quickly (however, in The Shining Darkness pack there will be a useful synchro for that situation Infernity Doom Dragon), thus lacking resources in case his/her plans goes wrong (such as in the case the opponent counters a massive Swarming with a mass-destruction card like Torrential Tribute or Lightning Vortex). Also, although the deck is capable in itself of winning with a simple Beatdown strategy, its most impressive Monsters are Synchro Monsters, meaning anti-Special Summoning strategies will often work to cripple a Blackwing player's strategy. Blackwings can also fall to Shadow-Imprisoning Mirror as it will negate many of their powerful effects such as Gale's effect to halve ATK and DEF. Blackwing's swarming can be stopped by Summon Limit. Koa'ki Meiru can also hinder Blackwings in many ways. Also, in the OCG and now in the TCG, there is a new anti-dark card, Consecrated Light. Royal Oppression can also negate the Synchro summoning of the Blackwings (however, it is unable to negate Shura's effect because it activates during Damage Step and it cannot prevent Synchro monsters that are Special Summoned using Vayu's effect since Vayu does not involve paying a cost). Most Blackwing Support cards require a Blackwing monster to be on the field (Icarus Attack being among the top choices). A well played Trap Stun or Royal Decree can shut down these traps and place the opponent at a disadvantage. Mask of Restrict is exceptionally good at stopping Icarus Attacks. Summon negation counter traps like Forced Back can prevent Blackwings from hitting the field and utilizing their Spell and Traps that require Blackwing field presence like Icarus Attack, Delta Crow - Anti Reverse, Black Whirlwind or Swallow's Nest.

Blackwings require the initial normal summon to the field to start field presence negating that summon or immediately destroying that monster with a Trap Hole or similar card will prevent swarming for that turn.

Siding in Blackwing - Sirocco the Dawn is also surprisingly effective against Blackwings, since Sirocco can use the opponent's Blackwings for his effect.