Oh, interesting. Terrence had used animals in the duel, but these people could become animals. Animagus abilities had never really crossed his mind, except briefly, because in a duel he felt his wand was more useful. However, he could now see that it could sometimes be very useful.
He was still sending hexes flying at the three of them when the second one transformed. It was a dog, which could surely sniff him out, even though he was invisible. With an easy movement, one of the knives at his free wrist was in his hand; he could throw it if necessary, but the dog was a moving target. Terrence was still primarily using his wand, but if he was going to duel against something with teeth, he wanted a weapon he could use in close quarters. At least he had the advantage of being able to see the dog.
He wasn't going to make himself easy to find, still on his toes and moving quickly, even though that helped him more against curses than Animagi.