After your postcombat main phase, there is another upkeep step
Then this 5/5 costs 7, and has a trilogy of key keywords that are awesome together - haste to get a faster Commander Damage kill, flying to swing over ground pounders, and then vigilance to swing and stay back for the blocking
You'll choose the target instant or sorcery card for that second ability at that time, based on the value you chose for X
If you win the flip, but the spell that caused Krark's triggered ability to trigger isn't on the stack anymore (most likely because it was countered), the copy is still created
The video mentions the official name of the A2a expansion, "Triumphant Light," and several new cards coming to the game
I have no idea what the correct balance for the four aforementioned cards is, but having more pieces in our toolbox to fully streamline the deck cant be a bad thing