It's a Red Scooter Blenny (so-called, it ain't a blenny at all) Synchropirus ocellatus I think is the scientific name.
Like all dragonets they are picky eaters and prefer pods etc found on Live Rock. However, they are much easier to convert to substitute live foods like BBS and bloodworms and eventually to frozen foods than are Mandarins. From all I read the latter usually starve to death sooner or later after purchase, so I am not surprised that you lost yours.
This guy will eat anything now, apart from flake.
The red scooter has an incredibly beautiful dorsal fin that looks like a decorated Japanese kite or lantern when extended, but I have not yet been able to catch him on camera while he is displaying it.
These guys are in my 15 gal Nano, but the sandsifter goby will eventually go over to the 55 since he is getting kinda big.