Can Riposte be used to counter your own spells?

Ruling: Yes, Riposte can counter your own spells. The card says "counter a spell" without specifying "enemy spell," so it can target any spell including your own.

Nuances:

• Riftbound card text is very literal - "a spell" means any spell, while "an enemy spell" would specifically mean an opponent's spell
• If a card doesn't specify a restriction and it doesn't violate core rules, the action is allowed
• This may only be viable in edge cases where it's the only play available to win