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.
I don't like writing so this is going to be short.
Madreds makes you do good magic damage to anyone as well as some armor and attack damage.
Malady gives you some ok ability power and helps keep their magic resistance lowered which makes Wit's End, Sword of the Divine, Malady, and Madreds more effective.
Frozen Mallet gives you some nom nommy health and a guaranteed slow on attack plus some additional attack damage.
Wit's End for magic resistance and its ability to kill mana, effectively making carries unable to cast any of their abilities.
Sword of the Divine gives you a boat load of attack speed as well as an awesome passive for damage as well as an awesome active to fight against Jax.
Mercury treads give you some magic resistance as well as its wonderful passive.
Wit's End, Sword of the Divine, Malady, and Madreds all give you some great attack speed as well as providing magic damage on hit. Combined with your Toxic Shot, your enemies will crumble before you.
This build is great against carries as well as anyone that stacks a lot of armor (i.e. Rammus)