In our Curse of Strahd campaign, the group's Paladin has just hit level 5 and is requesting that I, as the DM, would allow him to summon a Giant Owl for his Find Steed spell.
The spell does say "Your DM might allow other animals to be summoned as steeds"; however, none of the creatures listed have flying speeds, and I'm afraid allowing this might result in unbalanced encounters. That plus the Giant Owl's 60-foot flying speed and Flyby ability essentially eliminating opportunity attacks sounds ripe for exploits.
Are my worries accurate? Would allowing a flying creature for Find Steed cause problems?