Farewell is strongest when all modes are used, but the caster can pick just one or two if they choose, making it a bit overcosted for its effect but more flexible
As new sets are released and the game evolves, certain cards may see a rise or decline in value
Being this large for this price at the time was an outstanding deal, even if nowadays it doesn't look like much, and the bonus life points were like adding insult to injury, causing players to wince looking at their hand that little bit more and do it again when you cast additional black spells
Kill their creature on their end step and have a counterspell up on their next turn
If you were to control a card like Platinum Angel, then they cant win because the Angel specifically says so
If your creature with a counter on it has menace, it essentially makes them unblockable