Of all the non-interactive one-shot mungrel cards that make people want to leave the game, colossus is the worst (that still has avoided being changed)
It is fixable just reduce the damage in half.
Make it deal only ONE damage pass to the player+ minions, then another damage pass to minions.
The fact that it’s easy to copy the effect run two or even generate more means it already has a massive advantage, it make cthun look like a lemming.