Cast high-mana creatures quickly in Amonkhet Standard
Fastest I can get is turn 3.

T1: Mountain,  Bloodlust Inciter

T2: Forest, mana dork (e.g. Servant of the Conduit)

T3: Forest, Champion of Rhonas (give haste from Inciter)

Alternate:

T1: Forest, Loam Dryad

T2: Island, Thriving Turtle, Aether Theorist (off first Dryad) (or anything that gives 3 energy for 2 mana)

T3: Aether Hub, Aetherworks Marvel