Can I cast Fuel for the Cause on a spell that can't be countered (for example Thrun, the Last Troll) just so I can proliferate?
Can I cast Fuel for the Cause on a spell that can't be countered (for example Thrun, the Last Troll) just so I can proliferate?
Yes. "Can't be countered" doesn't mean it can't be the target of a counterspell - it just means that anything attempting to counter it will fail.
Fluttershy is best pony.