Because sometimes the party just ticks off a high level wizard and the GM wants something to chase after them. It’s going to be tough for a bunch of murder hobos to hide from something that can see invisible and is immune to illusions.

A hounds appear as large black hunting dogs with red glowing eyes and bat-like wings. A few powerful wizards have tamed these beasts to act as guards or send out packs of them to hunt down their enemies.
Armor Class: 6[13]
Hit Dice: 5
Attacks: Bite (1d6)
Saving Throw: 11
Move: 12 (Fly 24)
Special: See Invisible, Immune to illusions, Track by scent
Challenge Level/XP: 6/400

Roll Dice. Kill Monsters. Take Their Stuff. And have FUN!