Polymorphous Rush — ruling 1

The creature that's copied isn't targeted by Polymorphous Rush. You choose that creature as the spell resolves. It can be one of the targeted creatures. A creature can become a copy of itself this way, though this usually won't have any noticeable effect.

Polymorphous Rush — ruling 2

The target creatures copy the printed values of the chosen creature, plus any copy effects that have been applied to it. They won't copy counters on that creature or effects that have changed the creature's power, toughness, types, color, or so on.

Polymorphous Rush — ruling 3

If the creatures copy a creature that's copying a creature, they will become whatever the chosen creature is copying.

Polymorphous Rush — ruling 4

This effect can cause the targets to stop being creatures. For example, if they each become a copy of a land that has become a creature, the effect that turned that land into a creature won't be copied. The targets will become noncreature lands.

Polymorphous Rush — ruling 5

Effects that have already applied to the target creatures will continue to apply to them. For example, if Giant Growth had given one of those creatures +3/+3 earlier in the turn, then Polymorphous Rush makes it a copy of Pensive Minotaur (a 2/3 creature), it will become a 5/6 Pensive Minotaur.

Polymorphous Rush — ruling 6

You choose how many targets each spell with a strive ability has and what those targets are as you cast it. It's legal to cast such a spell with no targets, although this is rarely a good idea. You can't choose the same target more than once for a single strive spell.

Polymorphous Rush — ruling 7

The mana cost and mana value of strive spells don't change no matter how many targets they have. Strive abilities affect only what you pay.

Polymorphous Rush — ruling 8

If all of the spell's targets are illegal when the spell tries to resolve, it won't resolve and none of its effects will happen. If one or more of its targets are legal when it tries to resolve, the spell will resolve and affect only those legal targets. It will have no effect on any illegal targets.

Polymorphous Rush : règles, fonctionnement et interactions (MTG)

Polymorphous Rush 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

Strive — This spell costs more to cast for each target beyond the first. Choose a creature on the battlefield. Any number of target creatures you control each become a copy of that creature until end of turn.

How it works : Polymorphous Rush

Original English text — Wizards of the Coast / Scryfall

#1April 26, 2014· Wizards of the Coast
The creature that's copied isn't targeted by Polymorphous Rush. You choose that creature as the spell resolves. It can be one of the targeted creatures. A creature can become a copy of itself this way, though this usually won't have any noticeable effect.
No other card is named in this ruling.
#2April 26, 2014· Wizards of the Coast
The target creatures copy the printed values of the chosen creature, plus any copy effects that have been applied to it. They won't copy counters on that creature or effects that have changed the creature's power, toughness, types, color, or so on.
No other card is named in this ruling.
#3April 26, 2014· Wizards of the Coast
If the creatures copy a creature that's copying a creature, they will become whatever the chosen creature is copying.
No other card is named in this ruling.
#4April 26, 2014· Wizards of the Coast
This effect can cause the targets to stop being creatures. For example, if they each become a copy of a land that has become a creature, the effect that turned that land into a creature won't be copied. The targets will become noncreature lands.
No other card is named in this ruling.
#5April 26, 2014· Wizards of the Coast
Effects that have already applied to the target creatures will continue to apply to them. For example, if Giant Growth had given one of those creatures +3/+3 earlier in the turn, then Polymorphous Rush makes it a copy of Pensive Minotaur (a 2/3 creature), it will become a 5/6 Pensive Minotaur.
No other card is named in this ruling.
#6April 26, 2014· Wizards of the Coast
You choose how many targets each spell with a strive ability has and what those targets are as you cast it. It's legal to cast such a spell with no targets, although this is rarely a good idea. You can't choose the same target more than once for a single strive spell.
No other card is named in this ruling.
#7April 26, 2014· Wizards of the Coast
The mana cost and mana value of strive spells don't change no matter how many targets they have. Strive abilities affect only what you pay.
No other card is named in this ruling.
#8April 26, 2014· Wizards of the Coast
If all of the spell's targets are illegal when the spell tries to resolve, it won't resolve and none of its effects will happen. If one or more of its targets are legal when it tries to resolve, the spell will resolve and affect only those legal targets. It will have no effect on any illegal targets.
No other card is named in this ruling.
#9April 26, 2014· Wizards of the Coast
If such a spell is copied, and the effect that copies the spell allows a player to choose new targets for the copy, the number of targets can't be changed. The player may change any number of the targets, including all of them or none of them. If, for one of the targets, the player can't choose a new legal target, then it remains unchanged (even if the current target is illegal).
No other card is named in this ruling.
#10April 26, 2014· Wizards of the Coast
If a spell or ability allows you to cast a strive spell without paying its mana cost, you must pay the additional costs for any targets beyond the first.
No other card is named in this ruling.