Eldritch Duality

You have learned to anchor your mind in multiple realities at once, allowing you to maintain more magical focus than most mortals can withstand. Your eldritch patron has taught you to split your awareness without shattering it.

Expanded Concentration:
You can maintain one additional concentration spell at the same time.
You gain a number of Concentration Slots equal to your Wisdom modifier (minimum 1).
Each Concentration Slot allows you to maintain one concentration spell beyond the normal limit, up to the number of slots you have.

Concentration Check Scaling:
When you take damage while concentrating on multiple spells, you make one Constitution saving throw per active concentration spell.
You have advantage on these saves if your Wisdom is 16 or higher.

Mental Strain:
If you fail any concentration save, you must immediately choose one of your active concentration spells to end.
If you fail two or more concentration saves from the same source of damage, you take psychic damage equal to your Wisdom modifier + your Warlock level.

Patron Resonance:
Once per long rest, you can enter a state of heightened duality for 1 minute.
During this time, you may cast concentration spells without consuming Concentration Slots, but you still make concentration checks normally.