Does Stupefy draw a card immediately when cast if not countered, or only when it resolves? Can you hold priority to cast multiple spells in a row? When does priority pass after spells resolve on the stack?

Ruling: Stupefy draws a card only when the spell resolves, not immediately when cast. Any player can hold priority to cast multiple spells in a row, but must explicitly announce they are doing so (tournament rules assume priority is passed when casting a spell unless stated otherwise).

Sequence:

• When a spell or ability resolves from the stack, there is a new round of priority
• The player who controls the topmost item remaining on the stack receives priority first
• Players can hold priority after casting a spell to cast additional spells before passing priority
• You can counter any spell on the chain, not just the most recently cast spell

Nuances:

• Any player can hold priority (not just the player with focus or turn player), but must explicitly state they are doing so
• For Red Kai'Sa specifically: you can only conquer battlefields you haven't scored yet this turn