This list is just a opinion and aims to makes dead cards usable instead of nerfing op cards (because i don't think that there are dominant cards in the current meta)
Rage : Enraged troops deals 35 additional damage at TS, Duration reduced to 4,5s and not longer scales with levels.
This rework will standardize levels upgrades like freeze and makes it more versatile to use, It is also a nerf against high damage troops when paired with rage like ballon or elite barbarians with the decreased duration and the low damage added. It also makes big pushes more scary xd
Elite Barbarians : HP reduced to 760 HP, Attack increased by 15% , Hitspeed increased to 1,4s , Faster initial attack
This sort of rework will make EB having a better job at counter-pushing and would be better at defense overall with the counterpart of HP. It would die after a fireball+log or lightning, making it riskier to bridge spam.
Freeze : Damage reduced to 76 damage, Duration increased to 4,5s
Freeze is now even worse state than pre-rework as even with good plays, it does punish you to use it with the low duration. This buff would help you better with longer duration but doesn't kill fire spirit anymore. This may bring a alternative to fireball/ poison.
Heal : Heal increased by 110% , Duration decreased to 1s
Current heal even after post-rework doesn't seem to be used at all. I think one of the main reason is that everything outdamage the heal, making it useless 90% of the time. This change will make swarms less likely to be outdamaged and helps a bit with the additionnal 5% total heal on tankier troops now.
Arrows : Has now a Duration of 1s, troops inside are hitted 1 time only
Arrows are being overshadowed by other spells. His new ability would now pressure the opponent on attack by lasting now 1s and every troops inside it get the damage of arrow once even after placing arrows.
Lightning : Base damage increased by 10% Bolts increased from 3 to 4 , Each bolt have 20 % damage decrease after 1 strike (ex : First strike deals 100% Damage then Second strike deals 80 % damage and so on) you might say this is pointless, it's a balanced card but i think this card have a too similar roles with rocket and doesn't feel like a Epic card. This would make it trickier to use with the new gimmick but overall punish better big pushes.
Mirror : 1 Elixir decrease, duplicated troops are 1 level less than original. Dead card in normal matches, this would counter better bait decks especially the fireball bait decks.
Wall Breakers : Explosion radius increased by 2 tiles
They hardly reach the tower and doesn't seem punishing at all. By adding that, troops around the tower are now heavily damaged. It become a true high risk- high reward card
Personnal changes that i would also do :
Zappies - Faster initial attack, one of the worst cards for now
3M - Elixir cost decreased to 9 (again), 3m lightning is dead
Bomb Tower - Damage increased by 5% , still a underused card
Electro Dragon : Faster Initial attack , help him slightly as he is a niche card
Bomber : Hitspeed decreased to 1,6s , Radius increased by 0,25 , Attack act now like Dynamike's attacks from Brawl Stars