Hey mate, I saw your new video and it looks exciting! I love card collecting in games, it triggers something primal from my childhood. Have you thought about modelling the art of your cards off of tarot cards? Might be a fun way to add some mystique and creepiness.
I think some of the more interesting perks from Zombies have been the ones that fundamentally change a basic mechanic, like how PHD Flopper changed your dolphin dive into a weapon, or how Widows Wine gave a new use to your grenades. Perks that have multiple benefits are always fun too, they feel like you get more for your buck. Here are some ideas:
-Slow down time for a second when you get hit, with a cooldown.
-Melee attack does more damage, hits all zombies in front of you and pushes them back (kinda like a shove from L4D). The more zombies it hits, the less damage it deals, so your melee is now strong on single targets but has a utility against multiple targets.
-Landing a headshot on a zombie will increase the damage of the next headshot on that zombie (a stacking debuff). Landing a headshot on a zombie will momentarily reduce their movement speed. Zombies killed with a headshot will cause their head to explode and slightly damage nearby zombies.
-The player regenerates 1/4 of their weapon's ammo at the start of every round. Missed shots have a chance to be refunded. Reloading an empty weapon is faster. Weapons slowly reload while holstered. Picking up a health pack/grenade while the player holding maximum health/grenades will grant the player ammo instead.
-Using a health pack grants the player a shield that can withstand 1 zombie hit and lasts until the healing animation finishes. Grants the player an extra slot for health packs. Collecting a health pack while carrying max health packs will pay the player $500 instead. Maybe adds a funny or comedic healing animation to the potential animation roster.
-Grenades will split into three grenades upon being thrown. The player can carry more grenades. Grenades will stun zombies they don't kill. Reduces the damage to the player from grenades. The grenade animation is faster. Walking over a grenade while holding max grenades will pay the player $500 instead.
-A perk that increases the benefit of drops. Max ammos now grant a brief window of unlimited ammo. Quad damage grants more points per kill while active. Double points discounts the cost of the box and upgrading station while active. Full health will cause every zombie on the map to drop to half hp. Nuke will grant points for every zombie killed and delay the spawning of new zombies for a few seconds. Zombies will take more damage during time stop and move slower for a few seconds after it wears off. Allows drops to be rerolled once.
Your game is looking fantastic, I can't wait to see where you take it!