2019-06-14 : If Marit Lage’s Slumber leaves the battlefield before its last ability resolves, you won’t be able to sacrifice it, so you won’t create Marit Lage.

2019-06-14 : If you don’t control ten or more snow permanents as your upkeep begins, the last ability won’t trigger. No player may take any actions during a turn before the turn’s upkeep begins.

2019-06-14 : If you don’t control ten snow permanents as the last ability resolves, you can’t sacrifice Marit Lage’s Slumber.