Just wanted to share a list I've been playing recently I enjoyed and is actually quite cheap. Initially made it because I wanted to hit 5000 cards played with blue and purple, but it's been doing well for me on (champ) ladder as well. As any blue rainbow deck, you want to win with a burst of horn, usually with some enchantment buffs and overrun. Some things of note, particularly related to few-played cards:
- I really like the 2-drops with 4 health: Ravine Guardian and Little Crane Girl. They really are much better answers to aggro openings with pup or recruit. And with the coin from Rainbow's End you can always answer their 1-drop. Moreover, the 4 health makes them ideal targets for a turn 3 Godsblut. Ravine Guardian is good versus valkyries as the 3/4 statline usually needs 2 trades from their side
- Little Crane Girl obviously synergises with the Pentacle of Flavors, creating great board control, but also on a Stairway she can get around chump blockers
- The Shinobi of Smoke can really bully the board if they don't have rush or spot removal. I very much like to coin Shinobi, to follow up with a Barkeep or Fossegrim to teleport and make a value trade.
- Of the enchantments, Pocket Instance is not often played, but has actually been very useful. The +1 attack and alpha strike usually means a free trade-up that is not expected. Especially with all the movement that is in the deck. With the Shinobi, Pocket Instance and Odinthrone, there is actually a considerable amount of cards which allow to trade up.
The deck runs 4 mythics, but they are not necessary at all.
- Odinthrone can be any other blue enchantment (probably just a 3rd speedway, or a cairnhenge)
- Magnus can also be a Thunderclap, or another Jotun (or even some blue 4-drop minion like Timberland Troll)
- Waystone Garden can be any other enchantment. Preferably a purple one (like a 2nd Red Cliffs or Neo-Gangnam)
- Rogue Idolon I would replace with a purple 4-drop minion as there are already a lot of 3-drops (like Back Alley Ronin, Decoy or Thriving Shade)
The rares are a little more important, at least Allfather's Horn (must, it's your finisher), Pentacle of Flavours is very good with the 3-drops this deck runs (but less crucial), Fossegrim could also be a serpent (though you do lose a bit on the movement shenanigans).
Edit: small edits. Initially had 2x Five Spirit Gate, but changed to Waystone Garden and Red Cliffs