User blog comment:Lykrast/Reversing champions/@comment-4915885-20130127141712/@comment-5088437-20130127192108

I don't think Mega here was referring to just Karthus' ult.

Anti-Karthus, we'll call him, would essentially completely negate Karthus proper, and many champions probably. He'd also have no ability to solo whatsoever.

Still, amusing idea. Going with the 'not actually total opposite of their abilities' thought process,

Garen's Passive would grant additional health regeneration to all allied champions equal to .5% of their total health each second until Garen takes damage from any source except minions.

Garen's Decisive Strike would strike the allied target with his sword, healing them for 30 / 55 / 80 / 105 / 130 (+ 140% AD), removing any slows & silences, and increasing their movement speed by 35% for 1.5 / 2.25 / 3 / 3.75 / 4.5 seconds. This heal can critically strike.

Garen's Courage would increase all allied armor and magic resist around him by 20%, and activating it would grant all allies a defensive shield for a few seconds, reducing incoming damage by 30% and granting 30% crowd control reduction for 2 / 3 / 4 / 5 / 6 seconds.

Garen's Judgement would cause Garen to spin, healing all allied targets for 20 / 45 / 70 / 95 / 120 (+ 70% / 80% / 90% / 100% / 110% AD) damage every half second for three seconds, and 75% of that to nearby minions. This heal can critically strike.

Garen's Demacian Justice would heal a single allied target for 175 / 350 / 525, plus an additional 1 health per 3.5 / 3 / 2.5 health missing.

Oh, the carry is low on health? R.  Now you're back to full. Team fight? Spin & Courage thru your team, laughing off Karthus & Miss Fortune. AP Mid just got slowed/silenced by Cho'gath? Q.  Finally, a reason to build Garen super tanky.