Sniffer is the tracking hound pet of the Tracker. He resembles a dark Dobermann with glowing yellow eyes. This appearance of a hell-hound corresponds with his master's undead appearance, though it isn't specifically stated if either Sniffer or the Tracker are undead. Sniffer's keen sense of smell is a great asset to the Tracker in his hunts of targets even across dimensions.
Sniffer is never shown far away from his master in any episode the Tracker appears in. He is last shown taking part in the assault made by Phobos' forces toward Kandrakar in Y is for Yield. While the Tracker is killed in the series' finale, it's not shown what happens to Sniffer. Given the fact that his master's bats died along with him, the hound could have shared the same fate. If he survived, he was likely reimprisoned in the Infinite City along with the rest of the unrepentant villains.