Bat wings are a mount that you can buy from the crown shop for 7000 crowns. They increase your speed by 40% and you can have the for 24 hours, 7 days, or permanently.
Dropped from:
Rattlebones, +40% speed (1 Day)
Grubb(Boss), +40% speed (1 Day)
Kraken(Boss), +40% speed (1 Day)
Fairy Queen, +40% speed (1 Day)
Malistaire, +40% speed (1 Day)
Lady Blackhope, +40% speed (1 Day)