Goozim

Goozims are large, brown, hairy, seemingly carnivorous creatures native to Druelselstein.

Information
Goozims appear to be dangerous but capturable as a game in Druelselstein called "Poke the Goozim with a Stick" shows one being locked up and poked by civilians. Heinz Doofenshmirtz's unnamed father was the winner of "Poke the Goozim with a Stick" and received a Spitzenhound as a prize, which he named "Only Son" ("Got Game?").

A 2nd Dimension Goozim is later used by the 2nd Dimension's Heinz Doofenshmirtz in an attempt to eat the 1st Dimension's Phineas, Ferb, Candace, Agent P, and Heinz Doofenshmirtz ("Phineas and Ferb The Movie: Across the 2nd Dimension").

Background Information

 * Goozims may be sentient or semi-sentient because if one listens closely when Heinz Doofenshmirtz's unnamed father pokes it with a stick it sounds as if it is yelling "OUUUCH" ("Got Game?").
 * The actual shape of the Goozim may be a square, but that is unknown for sure, seeing as it appears to take on the shape of its environment (eg - a square cage, the cylinder portal) ("Phineas and Ferb The Movie: Across the 2nd Dimension").
 * Goozims don't appear to be very strong for their size, as the Goozim cage depicted in Got Game? doesn't look very strong. However, in the 2nd Dimension, the Goozim cage is shown to be made of iron, indicating that in the 2nd Dimension, Goozims may be much stronger than their 1st Dimension counterparts or the iron could just be the only mineral there to use ("Phineas and Ferb The Movie: Across the 2nd Dimension").