What’s the consensus on the rules of the game for the chosen card?

Would a Cards Against Humanity black card, which does not require mana to play, be playable? Would other players have to ‘respond’ with a card from their hand?

If you get multiple of these (or recall from graveyard) can you play the card if you also bring in the activation mana/cost whatever?

Is mana equitable across games? If you pull a card from a game that uses the same color mana as your deck, can you play the card? (For example, the game Not Enough Mana uses blue mana that is represented by a water drop.)