So, Vi
Put simply, death itself, if you play her right.
Lets get on with it, so you can kill Jinx and rub her face in her failure.

So, Vi (again)
Mobile, Armour-shredding, harassing through basic attack, immune to cc.
That's basically it

When Vi-ing, basically wait for your team to be behind, and a squishy carry to misplace themselves. Ult in, then q immediately, because, as few people know, your ult places you behind them, and a q can knock an enemy forward. E when you can catch multiple enemies in it, and basically run away when on low. Try to be bait, as you have a very reliable escapes, and are quite tanky with this build.

Same principles, except you might need to misplace the carry yourself. My tactic is attacking the carry when they are alone, with a team mate nearby. Run when at 50% health. Then Q over a wall, and they will dash (like lucian or graves) or flash over. Q them into the wall, and if they get back over the wall, ult onto them, and they should be dead by now. Try to only do this in warded areas, and without enemy teams. If team fighting, hide nearby, positioned on a flank. Q over a wall as soon as you see the opportunity, and read through the previous chapter again on what to do next.

Pros:
Can be built assassin, fighters or tanky.
Fun to play.
Reliable engages and escapes.
Eats tanks and squishies.
Cons:
Hard to play
Can get behind
Gets ks'd a lot (in my experience)

Start at krugs. Take red often. Give blue to midlaners. As for counterjungling, do it. Take their reds, and give their blues to midlaner. Then you can give you red to the ADC and the blue to the supp.

Nothing unique about vi, passive shield, on hit armour reduction, immunity to cc...
Doesn't matter. you can still eat most people if you play right