I know meta magic is not a D&D thing but I found it quite fun in pathfinder, albeit in those games the power scaling is very different. We ain't killing gods here. So I reworked these ideas to make them viable for our current adventure path / power.

1) Heighten Magic: without mythic power giving you the ability to be a God, lifting level 1 spells to lvl 10 is broken. But being able to do the opposites may be possible. So I propose Dampen Magic: cast a spell at a -1 level. I propose this reduces spells power by 1 category. Or 10% whatever is higher

2) Reach Magic: we already have eagle eye in 5th edition. Make it work with spells.

3)Selective Metamagic: not op. Just make it cost +2 spell levels over pathfinder +1. To avoid more cheese.

4) Maximize: no chance way to op. Unless it's +3

5) Element: convert: reduce Magic damage by 50% if any element-75÷ if element is force.

What do you think about it