Caves of Chaos Adventurer

You cannot venture into Undercity unless instructed to do so, either because you have the initiative at the beginning of your upkeep or because you take the initiative. Notably, if you aren’t in a dungeon and an effect instructs you to venture into the dungeon (not venture into Undercity), you can’t start Undercity.

If you aren’t in a dungeon when instructed to venture into Undercity, you will put Undercity into the command zone and move your venture marker to Secret Entrance (the first room).

The initiative is a designation a player can have. A player with the initiative designation is said to “have the initiative.” The initiative carries two inherent rules. First, whenever a player takes the initiative, and at the beginning of the upkeep of the player with the initiative, that player ventures into Undercity. Second, whenever one or more creatures a player controls deal combat damage to the player who has the initiative, the first player takes the initiative. Also, some abilities will refer to having the initiative and provide other benefits.

A player who currently has the initiative may take the initiative again. This causes that player to venture into Undercity again, but does not cause them to have multiple initiative designations.

Caves of Chaos Adventurer's last ability checks to see if you've completed a dungeon at the time you exile a card. If you haven't completed a dungeon at that time, you can't cast it without paying its mana cost, even if you complete a dungeon later during the same turn.

If you have completed a dungeon when Caves of Chaos Adventurer's last ability resolves, you can only play the exiled card without paying its mana cost. You can't choose to play it normally.