This Zuka is not the original Zuka, but rather just a shard of him. This particular shard of Zuka is the shell of him, the remainder that other other pieces go back into.
This shell can be seen in the drawings: Grump, Return, Z1-13, and Ascension. This shell has also written notes on Cassandros, mysterykid, and himself. This shell also has the 1X1X1X1 brick and The Void Star, the two objects needed to trigger ascension with Ember. Upon his ascension, he merged with Minish, Ember, and Kindle to create "Zukember". This fusion is currently deceased. The original Zuka was shattered by Dignity whom was possessed by X. The event can be seen in the drawings Zuka, Minish, and Dignity.
In the drawing Keys, he is represented by The Void Star.