Use a cards effect Some Leader or Character cards have effects that can be carried out during the main phase
Get enough Persistent Petitioners in play, or make a ton of copies of them, and youll quickly be milling your opponents out of the game
Back in the day, if you sat in a pod and one of the players had Zur the Enchanter, it immediately became an Archenemy game against them
Miku, Child of Song This card is a pretty powerful 6/6 legendary creature, but it takes a lot of mana to play
----- Flying Whenever Balamb Garden attacks, draw a card
Thraben Inspector is a perfect example, giving you a cheap body and a Clue token to crack later for more cards