Sergeant Tin is a snake and officer of G.U.N. in Sonic the Comic Online. He is generally very professional in his duties, but seems to be slightly embarassed by his codename (though this may be down to Amy Rose being slightly flirtatious at the time). In Tin's defence, all the cool sounding metals had been assigned to other officers by the time he'd arrived.
In his only appearance so far in Sonic the Comic Online, he was assisting in the evacuation of children to the Miracle Planet. He would quickly be called into more dangerous action when a number of Tails Dolls activated and began causing havoc. Unfortunately Tin was brought down in a sneak attack from behind by two of the dolls, leaving Amy to fight them alone. After he recovered, he joined his fellows in cleaning up the Badniks' mess, but made a point of seeing Amy off before she returned to Mobius to warn them about the dolls.
Tin hasn't been seen since the events of Monsters on the Miracle Planet.