Maul of the Skyclaves — ruling 1

Attaching an Equipment with its enters-the-battlefield triggered ability isn't the same as using its equip ability. You don't pay mana for the attachment, and if the Equipment enters at a time you couldn't cast a sorcery, you can still attach it to a creature you control.

Maul of the Skyclaves — ruling 2

If the target creature becomes an illegal target, the Equipment remains on the battlefield unattached.

Maul of the Skyclaves : règles, fonctionnement et interactions (MTG)

Maul of the Skyclaves 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

When this Equipment enters, attach it to target creature you control. Equipped creature gets +2/+2 and has flying and first strike.(It deals combat damage before creatures without first strike.) Equip

How it works : Maul of the Skyclaves

Original English text — Wizards of the Coast / Scryfall

#1September 25, 2020· Wizards of the Coast
Attaching an Equipment with its enters-the-battlefield triggered ability isn't the same as using its equip ability. You don't pay mana for the attachment, and if the Equipment enters at a time you couldn't cast a sorcery, you can still attach it to a creature you control.
No other card is named in this ruling.
#2September 25, 2020· Wizards of the Coast
If the target creature becomes an illegal target, the Equipment remains on the battlefield unattached.
No other card is named in this ruling.