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)