Cave of the Frost Dragon
Land
If you control two or more other lands, this land enters tapped.
: Add 
.
: This land becomes a 3/4 white Dragon creature with [[ keyword: "flying" ]] until end of turn. It's still a land.
Johannes Voss
Rulings
If you turn Cave of the Frost Dragon into a creature but haven't controlled it continuously since your most recent turn began, you won't be able to activate its mana ability or attack with it.
(wotc • 2021-07-23)
If Cave of the Frost Dragon enters the battlefield at the same time as one or more other lands, it doesn't take those lands into consideration when determining how many other lands you control.
(wotc • 2021-07-23)
Printings
Rulings
If you turn Cave of the Frost Dragon into a creature but haven't controlled it continuously since your most recent turn began, you won't be able to activate its mana ability or attack with it.
(wotc • 2021-07-23)
If Cave of the Frost Dragon enters the battlefield at the same time as one or more other lands, it doesn't take those lands into consideration when determining how many other lands you control.
(wotc • 2021-07-23)