Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
This is a guide that abuses nuke damage on a short cooldown and insane damage over time. Singed is built very tanky to help keep kassadin alive while he unloads.
Basic mage runes on kass for obvious reasons. On singed i try to find a decent balance between tanky and ap for that crazy poison damage while hard to kill, this combination is meant to work well against almost any combo meaning singed has to absorb the damage if the enemies can dish it. He also takes move speed quints because his job is to toss and poison, movespeed helps him catchh people to toss and helps him avoid taking damage while the enemies follow his poison trail.
For singed grab improved ghost and ignite because ghost helps singed escape and run with his poison on slowly killing chasers the ignite is because two ignites in a lane is awesome. I also grab movement speed masteries as well as mana masteries in the utility tree. For kass i grab basic offensive mage masteries and mana in utility.
Kassadins items give him decent hp and a ton a ap. I usually play kass as an ap carry instead of the usual assassin that you see out of him. This build is very expensive but with this lane combo i usually walk out with 5-8 kills, yes this is that godly and consistent. Singed is built very tanky with mostly hp he ends with a good amount ap as well which helps that poison scale a little bit into late game.
Kass is very, very strong if you level the Q first. At rank one you can go for a first blood with it and it works well if your singed kites them with poison, against smart players they will not walk in the poison and you will probably just waste mana when they b. As you hit level three in your Q if you have continued to harass they will have one person around 30-40% health and at this point have singed run forward and grab a player meaning instant kill. If you get a rank in your W early you just are not thinking straight. Late game the W does wok with your high ap and your lich bane I hit ~450 damage then ~200 after when that is on. The skill just does not work the same early game. Singed is fairly obvious, grab poison for good damage and fling is some quick damage that gets quite significant, if you prefer W can be leveled second for a better slow giving more time to do damage.
Always take flash, its too good on everything. If you want grab the ignite but it could be replaced with exhaust but double ignite is a ton of early game damage and gets me about half my kills. For singed grab the ignite only if kass does as well and get ghost to kite with poison.