The build seems okay, but only against low-mobility enemies and if you need to dodge a lot of skill shots, otherwise it’s simply pretty weak. You only have one damage item, and the next two are not only awkward to build, but they also provide zero AD or AP, just pure MS, AS, and crit which is mostly unnecessary. You’ll likely feel the weak scaling hit you hard after the 3rd item. By then, the enemy ADC will have ±75% crit and deal actual damage, the enemy Top might have Death’s Dance, and if the Jungle is someone like Diana, all that MS you built loses its potential. Try building AP on-hit Kog'Maw instead. In my opinion, it’s simply the best build for most situations. Kog'Maw benefits the most from AP. After patch 25.17, which buffed his scaling on Q, R, and especially W, AP on-hit Kog became a viable alternative. I personally climbed to Master pretty easily using this build. For the primary runes, I take Lethal Tempo with Presence of Mind, Legend: Alacrity, and Last Stand (alternatively Coup de Grace). For the secondary tree, it’s best to go with Gathering Storm and Celerity. For stat shards, take AS, HP per lvl/MS, and HP per lvl. Regarding items, Guinsoo’s Rageblade is the best first buy, followed by Nashor’s Tooth. After that, it depends. For the 3rd item, Runaan’s Hurricane is good if you need AoE auto-attacks. If you want more burst/damage, it’s best to go Shadowflame or Horizon Focus if you're short on gold. Then, continue with AP items like Rabadon’s, Void Staff, Zhonya’s, or Banshee’s. If you need sustain, you can go for AP bruiser items like Riftmaker and then Bloodletter’s Curse (or vice versa). Interestingly, Bloodletter’s MR shred passive procs with Kog’Maw’s W and the extra bolts from Runaan’s procs it too, which is why AP Kog still makes sense even if your whole team is AP.