With White, we had a C-plus bunch. Blue only has two, so we’ll give these two as much attention as we can.
First of, 1U for a 2 / 1 is OK, especially at common. Being able to making a creature unblockable is also ok. Paying 4U for that ability isn't so OK. This reminds me of an Ally version of Amphin Pathmage from the Magic 2015 core set with a couple of elements switched around. The Pathmage was 3U for a 3/2 Salamander Wizard, but the ability to make a creature unblockable was only 2U. Basically you swap the Guide coming down 2 turns earlier for the cost of the ability. I’d prefer to play the Pathmage, honestly.
She’s probably filler in Limited, but the 5 mana unblockable ability could help you kill a player out of nowhere. At common, she won’t be hard to sneak into your draft deck.
Grade C (simply because unblockability out of nowhere can be good)
As we’ll see with many of the best Ally cards in the set, Halimar Tidecaller continues a theme of not caring about what other Allies are on board. This is a very interesting creature. Not only does she recycle any card with Awaken to your hand, she gives your creature lands flying. Not only does she consider awakened lands, but also gives your regular creature lands like Lumbering Falls and Shambling Vent flying, too. I really like the Tidecaller as she also has decent stats: 2 / 3 for 2U. She’s kind of a niche card, but seems playable in the right deck. Any Rally triggers you get in addition are gravy. The Tidecaller also has a really good friend with Noyan Dar, Roil Shaper in the set. We’ll get to him later.
Having an Awaken “lord” at uncommon is pretty awesome. This is definitely a build around uncommon in Limited and possibly Standard playable if Awaken becomes a strong Standard theme. Usually this will just get you back this set’s Awaken version of Cancel, Scatter to the Winds. That’s usually going to be good enough. Coastal Discovery at 3U is an overcosted Divination, but it’s another potential target. Clutch of Currents is a sorcery speed Unsummon that also has Awaken. Rush of Ice is half of a Send to Sleep. Both of those are one-drops, so they will probably be common choices. The coolest target would be Part the Waterveil, except that it exiles itself upon resolving. So Tidecaller has some decent targets in Blue alone.
Red does have a 1R sort of Electrickery in Boiling Earth. That’s it for Red. Green has Earthen Arms at only 1G, which has good synergy with Awakening lands by putting 2 +1/+1 counters on any target permanent. That’s also the only one in the color. Finally we have Roil Spout. It costs 1WU to put a target creature on top of its owner’s library. This Time Ebb effect is properly costed and should be a good card in Limited. It’s even better if you use it on an opponent’s Awakened land.
A lot of the Awaken cards are familiar effects that cost one more mana and some are a bit too slow at sorcery speed. Others are clearly decent. Tidecaller definitely has cards that work with her, especially Earthen Arms. Having the ability to use the Awaken spells for their regular effect earlier in the game and be able to have a second chance to cast them for their Awaken cost later in the game is pretty solid. Whether this will be an effect worthy of Standard play remains to be seen.
Grade B+ (with the potential to get better with additional Awaken spells in the format).
Verdict on the Blue Allies: B-/B+
While the average of these two is technically a B-minus, I bump the verdict all the way up to a B+ on the strength of Tidecaller, who I could probably give an A-minus just for being one of the best uncommons in the set. Having either of these two can force a somewhat awkward Blue splash if you’re going all in for Allies. But there are enough decent Awaken cards in Blue that you don’t even have to be on Allies for either of these cards to make your Draft deck. The Guide isn’t really good enough for Standard play, but Tidecaller may be. In any case, you want to pick Tidecaller as early as possible. Just being an Archaeomancer with a bit narrower focus is good enough, but giving Awakened or otherwise animated lands flying is just too much fun. Just make sure you have Noyan Dar in play for maximum effect!