“Games give you a chance to excel, and if you're playing in good company you don't even mind if you lose because you had the enjoyment of the company during the course of the game.” ― Gary Gygax
1. There is no restriction on who can use this global. It could be used by an attacker to prevent a blocker's ability triggering on a KO or on taking damage.
Unless called out specifically in the wording, globals can be used by either player.
2. Make sure to post exact wording when asking questions so others don't have to look it up when answering.
Spellbinding Circle wrote:
Place this die on an opposing monster. That monster cannot attack. Return this die to your used pile when the affected monster is knocked out.
The monster/character can not attack. They can still defend. Attacking and defending are distinct and never interchangeable.