duality buff: a ddl mutation, you can't use any objects, (if possible): pebble will throw you back from where you came.

negative buff idea: (idk if its a thing already) whenever you enter a room that has a shelter connection and isnt the same shelter you just slept in, all other connections lock forcing you to enter the shelter.

Duality Buff Idea - Scavenger Back Strength: If you can't hold back spears, you are now able to. In addition to that, you can hold multiple spears on your back (maybe 3?). Any spear above 1 makes you heavier.

noodle fly mutation make it when u get it you can turn your hands into spears and lunge forward

negative buff where a hurricane hits the entire planet for 1-5 cycles, the wind pushes you around and the rain is occasionally violent and also theres water in every room (shallow)

positive buff card: Dragon/lizard wings. works like vulture wings but lets you keep your hands. would be an unlock for a mission called Dragonslayer where you have to get the dragonslayer passage, kill a regular vulture and a king/miros vulture, and you have to get a decent amount of points from killing creatures (ex: 800-1000 points) the cards you would start out with in this challange would be as folows : Lightspeed spear , Wealth Is Power, Super Stomach, Aerial firepower, armed king vulture, and upgrader or multiplier

negative buff card: train lizards could appear in the game

suggestion for existing buff: make it possible to have certain limited buffs forever in the right circumstances, for example choosing scorching sun as a starter card will make it last forever sort of like a challenge.

The translation may not be accurate as it was translated via google translator.
I don't know all the buffs of this mod so some buffs may already be in the mod.
If I have any more ideas I will update this post.
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Negative buff: X2 spawnrate.
Negative buff: Rain will always start 25% earlier than usual.
Negative buff: All vultures are replaced by king vultures.
Negative buff: All vultures are replaced by miros vulture.
Negative buff: Slugcats can get tired like a gourmet.
Negative buff: Surrounds the slugcat with darkness in which nothing can be seen, but leaves a small circle in the center of the slugcat in which you can see normally.
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Positive buff: Tongue like a saint.
Positive buff: Slugcat gets bond mark.
Positive buff: Allows all slugcats to resurrect 1 any creature including slugcats once per cycle.
Positive buff: Permanently increases reputation with one group of creatures of your choice (lizards, scavengers, etc.).
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Neutral buff: All regular spears in the game are replaced with explosive spears.
Neutral buff: Removes all bombs, rocks, explosive spears, flashbangs and spore puffs but replaces normal spears with bug spears.

A few ideas: I don't know if any of these are in the mod (ive only played the mod for a couple hours so far), so if one of the suggestions is in the mod but I haven't encountered it yet, take it with a grain of salt.
Note: Will be updated when I think of cool ideas.
Positive
- Vulture Thrusters: You can hurl yourself in the direction you are facing (probably via jump + pick up while airborne), at the cost of becoming stunned upon landing. It covers a lot of ground and leaves the vulture smoke trail behind you.
- Blink: When throwing rocks, you teleport to where it lands.
- Fear The Fist: Slugcat cannot throw spears and instead and can double tap throw to punch a creature, dealing twice the damage of a regular spear. Has a chance to stun.
- Sticky Tounge: Saint tounge!! Can also double tap throw while crawling to launch it at any creatures you are facing to pull yourself towards them (or reel them in. Whichever is more fun).
- Bullet Time: Double tap grab while in mid air to enter bullet time for a short while. Doing this uses up a food pip. Similar to mushrooms but without the screen warping and it doesn't last as long.
SSSSSTYLE: Gain a sizable movement speed bonus after preforming a trick (sliding, backflipping, ect) or killing a creature. It would be funny if it displays the SSSADISTIC style graphic from ultrakill briefly (or alternatively just have a style meter, but I don't know how hard that would be). Also it would be funny if the card art is just a slugcat in the same pose as v1 in the ultrakill cover art.
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Duality
- Updraft: Random gusts of wind will launch you or a random creature in the room upwards periodically.
- Impulse Grenades: Grenades aren't fatal and instead cause creatures to ragdoll.
- Encumbered: You move slower the more items you carry, but deal more damage based on said encumbrance when falling on creatures.
- Gotta Go Fast: Game moves at 2x speed (stackable).
- Gravity Noncomplience: All projectiles aren't affected by gravity
- Scavenger Tax Collection Service: Scavengers gain joke rifles loaded with grenades to enforce taxpayer compliance.
- Infestation: All rocks explode into paincones.
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Negative
- It Hides: All creatures can cloak (like white lizards).
- Taste The Rainbow: When it begins to rain, lizards start falling from the sky.
- Rubber Bullets: Enemy projectiles ricochet.
- Minefield: The ground where you step explodes after a few seconds.

Overkill (positive): If you deal damage to a creature that it already dying or dead, the damage that you would've dealt to them is added to your next spear attack that you do.
ULTRAKILL (duality): rocks no longer deal damage and have a large upward arc. However, hitting a thrown rock mid-air will make your spear automatically target the weakpoint of the nearest enemy, and the spear will deal 2x damage. (basically just coins from ULTRAKILL)

Positive buff: hard-headed, stackable (the player has a chance to deflect any spears if the spear hits their head, the more of this card, the higher the chance to deflect the spear)

I got a few ideas inspired by other games
insta-shield: basically, upon triggering, projectiles get deflected, and creatures next to you take 1 damage, however it lasts for an insanely short period of time. getting additional stacks will increase the shield area and give the potential to reflect projectiles back at the attacker. Overwritten by any other ability that is activated in the air.

speed shoes: similar to butter feet, however you gain more speed as you keep running, but the more speed you have, the harder it is to stop. Running into a bump that you would climb over by pressing jump will trip you if you move too fast. Going fast enough may allow you to run across water.

hitscan: all projectiles travel very fast, however do the same amount of damage and effect. affects all projectiles.

ground pound: pressing an input in the air (might be down, might be a keybind) will cause your slugcat to pause in the air, then fall downwards fast, dealing a set amount of damage if they hit a creature.

Batter: spears become melee weapons, being swung in an arc, rather than using its pointed end. This causes it to be able to deflect projectiles, and deal greater knockback and stun, however spears will do less damage. Maybe holding some direction when swinging will change the type of swing, like being able to beat down stunned creatures?

escape timer: you must plan which shelter to go to when starting a cycle. When you get halfway to the shelter, a timer will start, which is essentially the same as the buff that kills you after 200 seconds in a cycle. Backgrounds may be distorted when the timer is started as a little nod to various games with escape timers.

explosion immunity: makes you unable to be hurt by explosions (may also apply to any modifications to explosions done by other cards), however you get launched further by them.

choosing sides: all creatures with reputation will have their reputation with you passively increased no matter what, however any other creature that attacks slugcats when unprovoked now target you.

long jump: slides are replaced with instant slide pounces, with the attributes of a slide (such as abilities activated with slides)

triple jump: jumping three times in a row while moving will make you jump higher each time.

confusion: sometimes, when holding two items, you'll throw from the wrong hand. This also applies to eating things, which can either stun you from hurting, or have more... disastrous consequences, such as with a scavenger bomb.

venom: dealing a damage to a creature will cause it to slowly lose health over time. more effective if inflicted by mauling.

gotta go fast edition: the more pips you have filled, the faster you will go. The effect will be stronger if you have more pips in total, however you start slower than normal at no pips. inspired by the rom hack sonic 1 gotta go fast edition, hence the name. you could also see it as being similar to karma appetite.

vault: you can press a kaybind (or a button combo) right next to a creature to vault off of them, sending you into the pounce state and letting you jump noticeably higher than normal. if you can body slam, this will damage the creature you vault off of as well.

metallic: using a keybind, you can heavily fortify your body, heavily reducing movement abilities but increasing weight, survivability and knockback/stun resistance. you're also immune to being harmed by electricity and even get buffed by being zapped in this state. has a cooldown and lasts for a short time.

bullet dash: similar to an alternate ori bash, instead of just bouncing off a target, you barrel through the target, dealing damage without launching it in the opposite direction, however you still go where you were aiming. Cannot be used on projectiles, even when upgraded.

speed down: walking speed is lowered, however other methods of movement are unaffected.

deer mutation: you can only hold things in your mouth, however, you gain much longer legs that extend when holding up and fold when holding down. you need to be fully lowered in order to crawl, and your diet gets changed to mainly plant-based, however you can also eat spore sacs. If you get stunned, you fall to the ground from whatever height your body is at compared to your legs. you also can extend your legs to go over wormgrass, or are simply immune to it.

creeper: similar to unstable slug, except it is activated on command and launches you instead of stunning you (or maybe both?) Inspired by both minecraft creepers and the bob-omb partners of the first two paper mario games

arti blast?

like the jump thing
unless thats already there