While I'm of the opinion that Yurlok of Scorch Thrash will be flat out over-powered and dominate the board whenever it comes down. But more important than its power is that I think it's a pretty uninteresting power (set it down and blast the opponent for 6 every turn). I want Ziatora's Envoy to be a card that complicates combat- either forcing a block or providing card advantage to colors that don't excel in the late game without it. Very likely, I'll end up making this exact exchange later, precisely because Envoy is less powerful but more interesting.