Polymorphist's Jest

Polymorphist’s Jest overwrites all previous effects that set the creatures’ base power and toughness to specific values. Any power- or toughness-setting effects that start to apply after Polymorphist’s Jest resolves will overwrite this effect.

Polymorphist’s Jest doesn’t counter abilities that have already triggered or been activated. In particular, there is no way to cast this spell to stop a creature’s ability that says “At the beginning of your upkeep,” “When this creature enters the battlefield,” or similar from triggering.

If one of the Theros block Gods is affected by Polymorphist’s Jest, it will be a legendary 1/1 blue Frog enchantment creature with no abilities. If it stops being a creature, perhaps because your devotion to its color(s) decreased, it will be a legendary blue enchantment with no abilities. The way continuous effects work, the God’s type-changing ability is applied before the effect that removes that ability is applied.