Tranquility

Tranquillity is such a powerful card due to its consistency. Since it has retain, it means you can enter wrath more liberally than usual, as you have a backup plan in case you have no way of exiting wrath or finishing your opponent next turn. It can even be useful to play on the same turn as wrath after playing your attacks to prevent the enemy from hitting back as hard on their turn. The only downside to tranquilly is the fact that it exhausts - if this is your only source of calm, you will only be able to enter it once. For this reason, it is not uncommon to pick up even 2 copies of this card in addition to other sources of calm such as vigilance.