Startling Development

2020-04-17 Because damage remains marked on a creature until the damage is removed as the turn ends, nonlethal damage dealt to the target creature may become lethal once its base toughness becomes 4.
2020-04-17 Effects that modify the affected creature's power or toughness without setting it will apply no matter when they started to take effect. The same is true for counters that change the creature's power or toughness.
2020-04-17 Startling Development overwrites all previous effects that set the affected creatures' color, creature types, power, and/or toughness to specific values. Other effects that set these characteristics to specific values that start to apply after Startling Development resolves will overwrite that part of the effect.
2020-04-17 The affected creature doesn't lose any abilities when it becomes a Serpent.

Card is in preconstructed decks:

mtg.wtf