The wolves appear in the episode One Good Scare Ought to Do It! They are a part of the haunted house that Phineas and Ferb build to help Isabella with her hiccups.
The three wolves were one of the first horrors in the house. When Phineas and Isabella past them for the first time, they were gnawing on some bones. When both left the room the three wolves howled together. When Candace enters the house later the three wolves are escaping the collapsing mansion. It is unknown where they are now.
The three wolves are dark gray with fierce green glowing eyes and giant razorsharp teeth.