2016-01-22 : 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.

2016-01-22 : Gift of Tusks 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.

2016-01-22 : Gift of Tusks 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 Gift of Tusks resolves will overwrite this effect.

2016-01-22 : If the affected creature gains an ability after Gift of Tusks resolves, it will keep that ability.

2016-01-22 : 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.