User blog comment:Willbachbakal/(Champion Rework) Singed, the Mad Chemist/@comment-1920550-20150515080443/@comment-1330314-20150525192621

It's likely an optimal build would involve building tanky, and perhaps a bit of AP and mana on the side. The end result shouldn't be too different from his current build, though his health would come from tanky items and his own base stats rather than his mana.

The idea behind moving his Poison Trail to his ultimate is to prevent him from proxy-farming, at least during his first few levels, and to give him more things to do during the laning phase, since his current Q makes it difficult to initially last hit and interact with opponents. As you mentioned, Singed's current ult is just a pile of stats, and isn't a particularly interesting ability to use, and because of that I think Singed needs more things to do during teamfights besides run around and annoy people. In order to achieve that, I gave him abilities that would modify his Poison Trail, and for that as well it would be better to make it his ultimate, rather than a basic ability (it's also his most iconic ability).