This is a special ability - which could be a static effect (Jinx's Loose Cannon legend draws you an extra card if you start the turn with one or less) or an activated ability (Darius's legend taps for 'mana' if you've already played a card that turn)
Especially where it includes playing for cash prizes (e.g., MagicFests and professional level events) and allowing people of all ages to take part
The first is to destroy any creature or planeswalker, making it a Hero's Downfall for one more mana
Conversation has mostly centered around cards like Imperial Recruiter, Chalice of the Void, Rishadan Port, Eidolon of the Great Revel, or even today's filter lands
3 Celestine, The Living Saint - Forces Of The Imperium Despite the wings, halo, and a massive golden sword, Celestine, the Living Saint is a powerful human commander with tons of creative interactions with lifegain mechanics
For master-set builders, this is the finish-line card