Dauntless Dourback: The talisman of the treefolk deck. This card wins games.
Dungrove Elder: Modern isn't a very forgiving format, but the hexproof makes it more than worthwhile. It lacks trample and is weak the deathtouch, however this card can close out the game against removal heavy decks.
Harmonize: This card isn't really common in modern, but the massive card advantage in green is too good to pass.
Treefolk Harbinger: An amazing tutor and great to disable Goblin Guide on turn one. This card can find fix any holes in your opening hand, or find the perfect card for any board state.
Timber Protector: Very expensive at 5 mana, but has one of the most powerful lord abilities in the game. Its a great followup play after dropping a big threat.
Lignify: Very suboptimal removal, but its a flavor win.
Elvish Mystic: While it isn't a treefolk, its still on flavor and really helps dishing out big threats early. There are better mana dorks available, but the mystic is great for the budget, and gets the job done.
Sakura tribe elder: Very nice ramp which boosts the big treefolk, and also receives the buff off of bosk bannerett. A great ramp option that could also save a few points of damage.
Bosk Bannerette: Fits perfectly with the deck and makes everything easier to cast.
Leaf Crowned Elder: The ultimate value treefolk. Although its a magnet for removals cards, its a nice threat and fells really good dropping a free treefolk.
Forest: While splashing white for removal is tempting, I'm trying to keep this budget friendly. Since treefolk care about forest on the battlefield, I won't add any special lands.
