When you fight the Warlock it says lf you pass a Combat check against the Warlock, return it to the box & gain 2 Clue tokens.

Does this mean as it has 2 toughness & you roll 2 sixes that the card is removed from the current game & you get 2 Clue tokens or does it mean you only have to roll one 5 or 6 to return the card to the box & collect 2 Clue tokens.

You have to pass the Combat Check as normal (as with any other monster; in this case, 2 toughness = 2 successes), but instead of taking the Warlock counter as a trophy, you toss it in the box (out of the game entirely) and gain 2 Clue Tokens instead.

And by the way...Welcome to the Carnival, alboy!

The combat check's difficulty is equal to the monster's toughness. Passing the check means killing the monster. The special ability just means you get 2 Clues instead of a monster trophy.

Thanks for the welcome & help.