The new-ish Symbiosis ability is actually really good for an effective Scoia deck when pared with the Nature's Gift faction ability. When building, search for "Nature" first, and use just about each of those cards, and then search "Symbiosis" and add all those cards. Add Forest Protector, which can reuse a spent Nature's Rebuke for a 5-damage removal card, plus 2 boost to a treant on your side. Additionally, Hamadryad not only has Symbiosis, but it boosts itself conditionally when it has Vitality, which means the benefit from Nature's Gift become 12 boost rather than 6 boost, and it synergizes with Dryad's Caress, Ida Emean Aep Sivney, and Shaping Nature.
You will want to use only Scoia'tael cards for this deck to get the benefit of Eithne Young Queen's Devotion ability which allows Eithne Mother to tranfsorm into Eithne: Wrath of the Brokilon, giving the benefit of having Symbiosis on top of the 2 Young Dryads that are spawned in the row.
A major weakness of this deck is Geralt: Yrden, which'll reset a whole row's boost and totally takedown this strategy. Further, there are a handful of neutral faction cards that reset a unit, as well as 1 Northern Realms card and one Nilfgaard card. However, if you can get your opponent to use these cards in the first round, you can shoot for a third round victory. Other than that, try to split your card plays evenly between the rows to limit the negative impact of resets.