The second issue of IDW's Dack Fayden Theros comic was just announced, but until now we didn't even know what the promo card that will be included in issue one is. Apparently, all one has to do is ask to find out, sometimes - MTGSalvation Rumor Mill user jonnybgood23 sent IDW an email asking about the upcoming promo, and it was confirmed to be... High Tide, which is what Dack is sailing on on the cover for issue one.
Then, according to a post on Reddit, several other IDW promo images for upcoming Theros comics were found, including the confirmed High Tide. The others appear to be Acquire, Wash Out, Duress, and, for the second issue, Gaze of Granite (appropriately for the Gorgon confrontation).
These are all good cards - certainly not to the level of "too-good-to-be-true," maybe not as strong as the recent Turnabout, but all definitely Constructed-playable in some context, and all with quite nice-looking art.
Planning on checking out the upcoming comics for these promos? Let me know in the comments.