Pride Sovereign — ruling 1

Because damage remains marked on a creature until it’s removed as the turn ends, the damage Pride Sovereign takes during combat may become lethal if other Cats you control leave the battlefield later in the turn.

Pride Sovereign — ruling 2

Some cards in the Hour of Devastation set let you exert a creature as a cost to activate one of its abilities. You can exert it to pay that cost even if you’ve already exerted it earlier in the turn. Exerting it multiple times will keep it tapped only during your next untap step.

Pride Sovereign — ruling 3

You can’t exert a creature unless an effect allows you to do so. Similar effects that “tap and freeze” a creature (such as that of Decision Paralysis) don’t exert that creature.

Pride Sovereign — ruling 4

If an exerted creature is already untapped during your next untap step (most likely because it had vigilance or an effect untapped it), exert’s effect preventing it from untapping expires without having done anything.

Pride Sovereign — ruling 5

If you gain control of another player’s creature until end of turn and exert it, it will untap during that player’s untap step.

Pride Sovereign : règles, fonctionnement et interactions (MTG)

Pride Sovereign 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

This creature gets +1/+1 for each other Cat you control. , , Exert this creature: Create two 1/1 white Cat creature tokens with lifelink. (An exerted creature won't untap during your next untap step.)

How it works : Pride Sovereign

Original English text — Wizards of the Coast / Scryfall

#1July 14, 2017· Wizards of the Coast
Because damage remains marked on a creature until it’s removed as the turn ends, the damage Pride Sovereign takes during combat may become lethal if other Cats you control leave the battlefield later in the turn.
Card named in this ruling
Cat
#2July 14, 2017· Wizards of the Coast
Some cards in the Hour of Devastation set let you exert a creature as a cost to activate one of its abilities. You can exert it to pay that cost even if you’ve already exerted it earlier in the turn. Exerting it multiple times will keep it tapped only during your next untap step.
No other card is named in this ruling.
#3April 18, 2017· Wizards of the Coast
You can’t exert a creature unless an effect allows you to do so. Similar effects that “tap and freeze” a creature (such as that of Decision Paralysis) don’t exert that creature.
No other card is named in this ruling.
#4April 18, 2017· Wizards of the Coast
If an exerted creature is already untapped during your next untap step (most likely because it had vigilance or an effect untapped it), exert’s effect preventing it from untapping expires without having done anything.
No other card is named in this ruling.
#5April 18, 2017· Wizards of the Coast
If you gain control of another player’s creature until end of turn and exert it, it will untap during that player’s untap step.
No other card is named in this ruling.