DL Anniversary Birthday Cake is a Metal enemy found in celebration events that appear when the game reaches a certain download milestone, starting from 20 Million Downloads Special Gift!. Its appearance changes for every 10 million downloads.
An enemy with lackluster stats, it serves no threat and can be easily defeated. It does have a Metal trait to it, however.
Strategy
Using Cow Cat will defeat it quickly and efficiently. A Critical Hitter such as Merc, Catornado or 1 Million Dollar Cat can help you get rid of it sooner, but with 1 damage and less than 1 DPS, virtually anything can defeat it in the end.