Maokai: Morgana. BV, Hexdrinker, MR.
The ****??? Maokai's counter is Heimerdinger, or Swain. That is the counter to anyone who needs to get in close. And building MR against a tank? Seriously o.O
Janna: Kassadin, Akali. Gap-closer. BV.
The ****??? Why no Sivir? Why no boots? Why no Nocturne?
Karma: Akali. BV, Hourglass, Hexdrinker, MR.
Someone has never played Karma before. How about any AD carry? Seriously, if you have any knowledge of Karma, no matter who they are, Karma > Melee. Hourglass? Really? Karma virtually does sustained damage, and is a pseudo-support. And you suggest an HOURGLASS???
Rumble: Gangplank, Nasus, Tryndamere. BV, Hexdrinker, MR.
You gotta be trollin' me, bro... That sounds like a list of champions that Rumble gets fed from. And BV, against a champion whose primary source of damage is a conal non-debuff DoT. And whose instant damage skill can be shot twice.
Karthus: Soraka, Morgana, Nocturne. BV, Hexdrinker, MR.
Umm... yeah. Another case of 'I know nothing about this champion so I will put random stuff here'. Soraka only counters his ultimate, and only in the first few levels. Morgana... does not counter him at all. Nocturne... now that's just becoming stupid. Why no Gragas? Why no Janna? Why no Tristana? Why no Ezreal? Why no Gangplank? The main threat of Karthus is not his horrible singing, but when he walks/Flashes right into your team with no fear of death, causing death and destruction around him, finishing it off by singing. By that point, Soraka will be too dead to pray against his terrible 550 + 0.6 AP song. Get rid of him, or poke him to death outside the teamfight, and GG.
That's all I can see right now, although there are probably many more problems.