Heart of Crown

If I don’t have another card with a cost of 2 or higher in my hand, can I still play a Curse Witch (causing a misfire)?

You can play a card knowing it will misfire. The timing for using defense cards is very specific, and applies when you are resolving the attack’s effect on your opponent. In this example, they can learn whether the effect will misfire before they defend.
Related Rule(s)