Constellation

Constellation is an ability word introduced in Journey into Nyx, where it is connected to the god theme of the block.

Description
Enchantments with constellation abilities represent the divine constellations that fill the night sky and the mortal world of Theros.

An enchantment's constellation ability triggers every time it or another enchantment enters the battlefield under the player's control. Most of the enchantments with constellation abilities in Journey into Nyx are enchantment creatures, but not all of them.

Constellation was originally called Enchantmentfall. It was originally designed as an Azorius mechanic in Return to Ravnica, but it was thematically a better fit for Theros block.

Constellation returned in Theros Beyond Death. In this set, the ability word only appeared on non-enchantment cards, changing the dynamic into a enabler-payoff mechanic.

Oath of the Ancient Wood and Ajani's Chosen have a form of unkeyworded Constellation, as they were printed as plants for Theros block in Magic 2014.

Rulings

 * A constellation ability triggers whenever an enchantment enters the battlefield under your control for any reason. Enchantments with other card types, such as enchantment creatures, will also cause constellation abilities to trigger.
 * An Aura spell without bestow that has an illegal target when it tries to resolve will be countered and put into its owner’s graveyard. It won’t enter the battlefield and constellation abilities won’t trigger. An Aura spell with bestow won’t be countered this way. It will revert to being an enchantment creature and resolve, entering the battlefield and triggering constellation abilities.
 * When an enchantment enters the battlefield under your control, each constellation ability of permanents you control will trigger. You can put these abilities on the stack in any order. The last ability you put on the stack will be the first one that resolves.