Sadly, this 1/400 Big Zam from the Gundam Collection isn't listed in the Gunpla catalog.

Originally, the Gundam Collection was positioned as a series of figures, and it seems that some of the Mobile Armors and ships from that series have been made into 1/400 scale plastic model kits. It's characterized by being a pre-painted, semi-assembled model, which is probably why it's not in the Gunpla catalog.

The upper body is almost complete; you just need to insert the antenna and heat sink fins. After assembling the legs and nozzles of the lower body and attaching them to the upper body, it's a very easy kit to assemble.

046 It's sad, but this is war. | ヒロユキマル's Gunpla works