Just playing Arena using the Workshop:Heroes of Theros - Devotion deck.
I tried to cast Triumphant Surge when there was only my Transcendent Envoy on the battlefield. The Triumphant Surge just hung in the air over the stack part of the screen, not doing anything for about 10 turns. occasionally it would light up blue but mostly it sat in the way, I couldn't read the cards on the stack and didn't gain my 3 life. Then later in the game, when there was a legal target, I could cast the card by clicking on it where it was suspended on the rhs of the screen; it destroyed opponent's creature (4/4) and I gained 3 life.
Can I cast Triumphant Surge without a legal target to gain 3 life? Is this just a bug in Arena, or am I mistaken?