OHKO can be stopped by SoA and Damage Reduction, as people above said. Also, you can just pill enough to have 70 attack (unless the enemy has more than 12 pillz or has Hugo).
It's fun to put 2-3 pillz on Kolos (and no fury) when enemy has SoA or DR. He will probably 0 pill it and BAM! You just got 4-8 damage through with so little pillz
Kolos is badass. Very unpredictable. But the fact that people treat him as just OHKO card is a great advantage. Sometimes they forget that they already lost at least 2 life and think that I'm gonna fury my Kolos
Just use a soa or damage reduction like mrlambchopz said
To stop Kolos: Plan A DR (safest option), Plan B SOA, Plan C Power = Power.
I once had to use Plan C when Plans A and B are unavailable. When the opponent goes for the KO it's usually 9 pills (and 3 for fury). Use a Power = Power card and put 10 pills on it (there should be 2 pills left) therefore preventing the Kolos KO.
Note: Always works ONLY on Non-Random mode.
But using too many pills could backfire since the person using Kolos could use him as a bluff just so you'ld run out of pills
Thats happened to me a few times as well, where they used every card and saved Kolos for the end. I had my eye on the card the whole time waiting for them to play it but by the time they did I realized I had lost that match. Thanks for the advice everyone.
That's my strategy, and it's really really fun way to screw your opponent's mind around. XD