Thing in the Ice with 1 counter, Riddleform, and an instant. When you cast the instant can you get the conditional board-bounce and the sphinx or will Riddleform be returned to your hand if choose to let it trigger?
When you cast the instant, both Thing in the Ice and Riddleform will trigger. Since you control both triggers, you choose the order in which they go on the stack. If you put Thing in the Ice’s trigger above Riddleform’s trigger, you’ll remove the last ice counter, transform it, and resolve Awoken Horror’s trigger before Riddleform’s trigger resolves. Since Riddleform isn’t a creature when Awoken Horror’s trigger resolves, it won’t be returned to your hand.











