T-Rex is a dinosaur like Pyrosaur.
Due to the latest update T-Rex now only has a speed buff throughout its attack phase.
Keep in mind that the speed buff isn't as fast as some competitive pets.
T-Rex will headbutt anyone who comes into contact with it, sending them flying, similar to Boxing Glove.
Now due to the latest update the T-Rex does not attack throughout its whole lifetime but within the first three quarters.
T-Rex is a somewhat good pet but, due to the latest update, the T-Rex now attacks and has a speed buff for only three quarters of its lifetime and this may keep people away from it. It's not nearly as good as the Unicorn, though.