Balancing suggestions:

[Lobo23 2]

1) Girl power: make it area spell instead of single unit arcane
2) Warlock red: make him a t1 or increase dmg buff from 15% to 25% 
3) Warlock blue: make it as friendly unit takes less damage instead of the dmg buff against frozen units.
4) Color crystals: Affect color cards intead of affinities, and balance it accordinly and maybe even add mixed crystals (Fire crystal affects all fire units)
5) Ofering blue: Same as green, but instead of sacrifizing units it sacrifizes buildings
6) Rioters retreat: Should knock back small and medium sized units like its NPC counterpart
7) Also removing the 4 frost orbs requirement for coat of protection, regroth is more OP and it only takes 1 nature

[Ernecius 2]

Those are nice QoL ideas.

In the case of Rioter's retreat, the knock back could be too strong because right now the tower has a powerful support aura. I would suggest instead reworking Bandit launcher and move the rioter's aura to it, and then adding the knockback to rioter's retreat.

For coat of protection I think it's fine and a good reward to go full frost but the affinities should probably be removed since they don't add a sense of meaningful choice between them and I think pure, single element T4 cards should have no affinities since they're supposed to be a reason for you to commit to a pure deck and most of them are way too binary or problematic (Forest Elder, Batariel for instance).

The rest of ideas are really cool as that would help to make those relatively dead cards usable.