Climb Diamond tiers 3-1 to Mythic with this deck in BO1
Thorn lieutenant and Steel-leaf beat mono-red just because they force them into 2 for 1 scenario.
Vivien take car of mono blue, in part, but just to cast your stuff and out-aggro them lead more often then none to victory.
Mono white is treacky, but if you keep pace you will outmatch them because you have too many tools to draw and to grow your team. It often lead to a stalemate in midgame where you are just waiting for Vivien to utlimate.
Control is control. You have to be smart and to play them into a frilled mystic. Just do what you normaly do, but one step slower (meaning don't flood the board, it's better to force them to wipe the board with 2 creature than more). You have many ways to cast two creatures per turn and if you manage to slide a Banner on the board, it doesn't matter that they use their draw engine every turn, every creature you cast replace themself.
(This last line is good in every match up by the way, if your draw engine is on the board, you are going to have gaz to keep pace with your adversary. And the true draw engine of this deck is not Beastmaster, he is the decoy for your banner and Vivien. A sweet plus if he stick to the board, but yeah, realy just a decoy... )
Growth-Chamber is a realy lovely tool against control, if you recon you are playing again control I recommand to hold on to him until you have 5 mana, so you can answer a removal by searching for a replacement. You can also trigger removal with this card, because no one realy like to let you have another card advantage, adversary tend to kill him quickly or to counter spell him.
Finaly, Marwyn, it's a good card, if it stick to the board it's gonna make you cast your hand very fast. Meaning that you can play your hand by turn 3 with a Marwyn on board turn 2 (thank you Llanowar elves). Her combination with a clancaller and any other 2CMC elf will lead you to play a Vanquisher Banner or a Vivien Reid on turn 3 ! But don't expect to do that every game. You should better focus on adapting to your opponent then to try to pull it off with an aggressive mulligan, cause a lot of stuff kill marwyn, and i mean a lot !
And finally, the final piece of the puzzle for that deck to realy push it over other around him is the Frilled Mystic. The principal reason is that he is not suppose to be there, you will not play him in the early game, but when you have already empty mostly all your hand and you have a lot of mana available, he will be less obvious than usual, and you will snape an important play from your adversary. Viven can also help you find him, for dominance declaration or intimidation tactics (lol). Just be causious, you don't always need to counter Teferi or any other planeswalker, big flyers are more scary, enchantment like Ixalan binding is more dangerous, etc. You have Elves to clear the ground and to beat the adversary, you have a lot of them and they came in number, what Elves deck were lacking in standard was protection again magic, and the Mystic is there for you.
What realy made the deck possible is the addition of Unclaimed territory to help cast the 3 green of Steel-Leaf Champion and the 2 green-2 blue of Frilled Mystic.
Otherwise, the combination of good 2-drop and 3-drop creature, with the fact that you can start to draw everytime or so that you cast a spell, make this deck an ideal aggro type deck, with awesome mid-range to late game capabilities.