How useful would this ability be?

[Magikeeper]

As the title says, how useful/powerful would the below ability be? Let's assume:
> At will
> Level 6+
> Char can use this ability as part of some kind of special variant of extra attack. That means they can use it twice or use it with something else like a ranged attack or whatever.

Rejecting Glare
As an action, you can attempt to banish a target with a glance. Choose a creature or unattended object you can see within 60' of you. If the target is unwilling, it can make a charisma saving throw. On a success, this effect does nothing.

Otherwise, the target becomes partially intangible until the end of your next turn. While in this state, the target has resistance to all forms of damage, their weight is reduced to 1/10th of what it would normally be, and all damage they deal to other creatures and/or objects is halved (this does not stack with resistance, e.g. if an object has resistance to the target's attack their damage is only halved once, not twice). You can target yourself with this ability. This ability is a magical effect.

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[Citan]

As the title says, how useful/powerful would the below ability be? Let's assume:

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Hi! Seems your post went unviewed for some time.
To answer your question in one line: In my opinion, the effects described are worth a 3rd level spell at the minimum.

For a more elaborate answer:
- you make a creature gain resistance to all damage (aka 5x Protection against Energy + other spells I don't remember of) with the only drawback of dealing less damage. Compare with Warding Bond (2nd level), Protection From Energy (4th level), etc.
- also, this is not very clear how it should interact, and telling "it cannot stack with resistance" is both painful to manage and incoherent fluff-wise (you are basically depriving a target creature of a feature it has, although you are the only one affected by your spell).

If you really want to make this an at-will, at the very least, make it so that both you and the affected creature can not use any action (nor bonus action even maybe) while it is affected.
It makes this a very good "tank" feature for you, a decent save feature for allies, and a very good control feature against enemies (you spend all your efforts to completely block a BBEG actions while your friends mincemeat him).
Even like this, it may still require a resource such as a spell slot.