I'm a fairly new player as well, and it's always fun to see someone else building a U/g deck. I fell in love with the color combo back when gatecrash, and simic were released. I have a few pointers if you'd like.Are you too insistent on playing with only theros and beyond, or are you open to gatecrash cards?As far as theros goes: I'd do the following. Perhaps take out one Forest and one island to add in Nykthos, Shrine to Nyx It may not look like much, but late game a high devotion could lead to a monstrosity from it's second ability alone. If your goal is to draw more cards, I would consider dropping Nimbus Naiad and putting in Thassa's Emissary , and your Leafcrown Dryad would still offer something in the way of answers to flying creatures. Another great way to draw possibility would be the Bident of Thassa playing this right could lead to a high card draw for simply doing what you would be doing anyhow. If you do take this suggestion, consider adding Thassa, God of the Sea herself for some extra scry, and at a high devotion, an amazing creature. Also, consider replacing Nemesis of Mortals with Polukranos, World Eater Even though it may not cast as early if your creatures are dying, it can come out earlier if you aren't losing a lot of creatures. Not to mention it's monstrosity ability is much more versatile, and comes with a secondary ability that provides a possible solution to late game threats. Your curve isn't horrible, but could use just a bit of fine tuning. Perhaps four Sylvan Caryatid could not only leave you with a solid turn two drop, but also provide a sturdy manna ramp for the rest of the game. I find that removal spells prove to be one of the biggest threats to blue and green decks, so you could consider adding a couple more counters of some sort. I hope I have been of some help, instead of going too ADD in the past paragraph.If you'd like to see a few examples of what I've been rambling on about for the past minute or so, feel free to check out my blue and green deck. Although it only carries a few theros cards, it should show a decent manna curve example. (Un)Natural Selection I can playtest a few of my decks against this one later this evening and leave more advice if you'd like. Again, I hope I have been of some help.