Cheers,
there are plenty uncommons in Dominaria that are really good. What is the one you play the most and why? Or is there any mythic uncommon that’s incredibly powerful?
For me it’s Radha. I include her in my red and even green decks per default. You can dumb your hand literally every turn with three creatures on board. She makes bad swaps less devastating as they would be.
The Eldest Reborn and Time of Ice are pretty awesome control cards.
In Bolas’s Clutches is very useful as has not target objective. Also is legendary for my Thran Temporal Gateway.
Generally speaking, the legendary uncommons are really great cards, the sagas are very useful and i also use serra’s wings which also has a great value for a single support … Along with a first strike creature it is very handy.
Seconding Radha, but also a shoutout to Dauntless Bodyguard. Add it to any blocker and you can set up situations that are tough to get around, especially in some PvE nodes.
I’d say Seal Away, but that’s common!
Slimefoot is a boss. He gets big fast.
Tru dat, but Slimefoot is a rare 
Oh, shit, he is. He’s uncommon in paper. My bad lol
I agree on Eldest Reborn, it is a really cool card.
There is also Syncopate that I noticed on the card list, but don’t have it yet.
Name: Syncopate
Expansion: Dominaria
Rarity: Uncommon
Colors: Blue
Cost: 7
Type: Spell
Drain X mana from your opponent’s hand, where X is the number of Blue gems.
I don’t know if the text “drain” means you get the mana your opponent loses, like Kiora’s 1st ability
Tatyova is broken in the decks built around desert spells,
Sprout swarm is broken if you have slimefoot (12 power and toughness for 5 mana),
Clutches are amazing,
Yargle is very good being a legendary and enabling legendary spells, as well as closing out games extremely fast
Sorry, but ‘drain’ in censor, flusterstorm, frying sanity, and dreadwaters (in this last the gain mana is written apart) means just that the opponent lose it.
First time I read ‘drain’ I also understood what you said. A pity.
In Bola’s Clutches is insane. I’d say that’s the best uncommon I have. Oh my!! 
Chainer’s torment does what the mythic black pirate does but better.
Urogoros is a Dream Stealer everyone can have but with card draw.
And I almost immediately put Dauntless Bodyguard in my Gideon 3 deck. Prevent damage for blockers? Yes, please!
Serra’s Angel.