Shielding Plax — ruling 1

If the target creature is an illegal target by the time Shielding Plax tries to resolve, the Aura spell doesn't resolve. It won't enter the battlefield, so its enters-the-battlefield ability won't trigger.

Shielding Plax — ruling 2

This is not the same as hexproof. If, for example, you target one of your opponent's creatures, your opponents won't be able to target their own creature with spells or abilities.

Shielding Plax : règles, fonctionnement et interactions (MTG)

Shielding Plax 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

( can be paid with either or .) Enchant creature When this Aura enters, draw a card. Enchanted creature can't be the target of spells or abilities your opponents control.

How it works : Shielding Plax

Original English text — Wizards of the Coast / Scryfall

#1December 7, 2018· Wizards of the Coast
If the target creature is an illegal target by the time Shielding Plax tries to resolve, the Aura spell doesn't resolve. It won't enter the battlefield, so its enters-the-battlefield ability won't trigger.
No other card is named in this ruling.
#2April 15, 2013· Wizards of the Coast
This is not the same as hexproof. If, for example, you target one of your opponent's creatures, your opponents won't be able to target their own creature with spells or abilities.
No other card is named in this ruling.