Playground rulebreaks aren't fun
It's a trope at this point. That schoolyard moment where a kid who is losing declares they can't lose, because reasons. For reasons beyond understanding you continue to put that into your game. This is written in the context of a game that really serves to drill in the point. It was looking bad, down to half health already, but, a turnaround. Suddenly the losing player manages to creep back till they control the field, just one more turn and the game will be decided, what a twist. But, no, the now losing player plays an equipment that declares they cannot lose. No conditions, nothing they need do to maintain this state of invincibility, just have a creature to attach it to. They've no compulsion to attack or block, so, now the game gets to keep dragging out, the victor... Unvictorious unless they just so happen to have a way to remove the equipped creature. Oh, it's a white deck, so actually they need to have more kills than the invincible player has protections... Well... Isn't this fun... Now we wait for the losing player to find a way to win, not in dramatic fashion, simply because the game is not permitted to end any other way. And of course they succeed eventually through the, totally not poorly designed phyrexian monster, that can't take damage and reflects any attempts. Not even legendary so they can have several. How fun... There's nothing you can do if you're playing either of the two colours that only remove targets via damage.
****, my opponent can only be hurt by mcguffins, and I didn't pack any today.
Why add something to your game which can only serve to put a "have this specific answer that may not even exist in your colours or lose" card? You're game designers, you can do better than this