From Sonic Retro
Gold Beetle, ゴールドビートル, is a GUN robot that appears once in every stage of Sonic Adventure 2 and part of the Beetle series. Its essencially a Mono Beetle coloured gold. It has no attacks and the only thing it does is appearing for 3 seconds (?) when a character is near and then disappears, until either the character dies or one restarts the level. Most of the time their locations in Hard mode are the same as Normal mode (Metal Harbor), but there are cases where they shift positions slightly (Prison Lane) or disappear to a new place altogether (City Escape).