Turn to Frog — ruling 1

The creature will lose all other colors and creature types, but it will retain any other card types (such as artifact) or supertypes (such as legendary) it may have.

Turn to Frog — ruling 2

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

Turn to Frog — ruling 3

Turn to Frog 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.

Turn to Frog — ruling 4

If the affected creature gains an ability after Turn to Frog resolves, it will keep that ability.

Turn to Frog — ruling 5

Effects that modify a creature’s power and/or toughness, such as the effect of Titanic Growth, will apply to the creature no matter when they started to take effect. The same is true for any counters that change its power and/or toughness and effects that switch its power and toughness.

Turn to Frog — ruling 6

If one of the Theros block Gods is affected by Turn to Frog, 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.

Turn to Frog : règles, fonctionnement et interactions (MTG)

Turn to Frog is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Until end of turn, target creature loses all abilities and becomes a blue Frog with base power and toughness 1/1.

How it works : Turn to Frog

Original English text — Wizards of the Coast / Scryfall

#1July 18, 2014· Wizards of the Coast
The creature will lose all other colors and creature types, but it will retain any other card types (such as artifact) or supertypes (such as legendary) it may have.
No other card is named in this ruling.
#2July 18, 2014· Wizards of the Coast
Turn to Frog overwrites all previous effects that set the creature’s base power and toughness to specific values. Any power- or toughness-setting effects that start to apply after Turn to Frog resolves will overwrite this effect.
No other card is named in this ruling.
#3July 18, 2014· Wizards of the Coast
Turn to Frog 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.
No other card is named in this ruling.
#4July 18, 2014· Wizards of the Coast
If the affected creature gains an ability after Turn to Frog resolves, it will keep that ability.
No other card is named in this ruling.
#5July 18, 2014· Wizards of the Coast
Effects that modify a creature’s power and/or toughness, such as the effect of Titanic Growth, will apply to the creature no matter when they started to take effect. The same is true for any counters that change its power and/or toughness and effects that switch its power and toughness.
No other card is named in this ruling.
#6July 18, 2014· Wizards of the Coast
If one of the Theros block Gods is affected by Turn to Frog, 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.
No other card is named in this ruling.