It sounds like the character has the same total level as the rest of the party, but can only use features from half of those levels, so it’s going to be underpowered to the point of unplayability.
Just have two character sheets. Share equipment and at least the same constitution score so you can share hit points. It’s a few extra hit points than the Warlock should have but also it’s a pretty unique scenario. As long as they aren’t trying to cheese the system it would work fine.
This sounds like a fun character. They even balance it out by not allowing the two classes to operate at the same time so it’s not OP.
It sounds like the character has the same total level as the rest of the party, but can only use features from half of those levels, so it’s going to be underpowered to the point of unplayability.
Yeah, either give both the level or—IMO the better option—the GM can just give them level-ups twice as often. More work for the GM of course.
Just have two character sheets. Share equipment and at least the same constitution score so you can share hit points. It’s a few extra hit points than the Warlock should have but also it’s a pretty unique scenario. As long as they aren’t trying to cheese the system it would work fine.