Turn 1: Forest, tap for Arboreal Grazer, 2nd Forest out,
Turn 2: 3rd Forest, tap 2 for Incubation Druid, tap 1 for 2nd Arboreal Grazer, 4th forest out
Turn 3: tap Incubation Druid for 1 green, cast Stony Strength targeting Incubation Druid
-> at this point you have 7 available mana, more than enough to cast any big guys in the deck,
With perfect starting hand, perfect draw, and going second, it would be possible to have Impervious Greatwurm on the field by 3rd turn.
Starting Hand:
1. Forest
2. Forest
3. Forest
4. Forest
5. Incubation Druid
6. Arboreal Grazer
7. Arboreal Grazer
Playing the turns as outlined above
Turn 1 -> Draw Stony Strength
Turn 2 -> Draw Stony Strength
Turn 3 -> Draw Impervious Greatwurm
On turn 3 complete the steps above to get 7 available mana, then tap Incubation Druid for 3 mana, use 1 to cast the second Stony Strength, again targeting the Incubation Druid, re-tap the Incubation Druid for 3 more mana, bringing the total to 5, tap 4 Forests and one Arboreal Grazer (for convoke) to pay the 10 mana for Impervious Greatwurm.
Boom, 16/16 Indestructible, ready to attack the next turn!
*************Update*************
Found a way to get 37/37 with haste on 3rd turn.
Starting Hand:
1. Forest
2. Forest
3. Incubation Druid
4. Stony Strength
5. Leyline of abundance
6. Leyline of abundance
7. Leyline of abundance
Turn 1: Draw Stony Strength : Play 3 Leyline of Abundance and a Forest
Turn 2: Draw Stony Strength : Play Forest, Tap 2 for Incubation Druid
Turn 3: Draw Finale of Destruction : Begin the Mana production:
Tap Incubation Druid for 1 + 3 from Leylines;
Cast first Stony Strength targeting the Druid;
Tap the Incubation Druid for 3 + 3 from Leylines;
Cast Second Stony Strength targeting the Druid;
Tap the Incubation Druid for 3 + 3 from Leylines;
Cast the Third Stony Strength targeting the Druid;
Tap the Incubation Druid for 3 + 3 from Leylines;
This spends a total of 3 Mana and produces a total of 22 So you have 19 floating.
Tap the 2 forests and cast Finale of Destruction with X = 21, Search for Impervious Greatwurm, which comes on the field with +21/+21.
Result: Turn 3, 37/37 Indestuctible, Haste on the field!