I'd like to ask if you'd be able to make some of the effects a bit more "fair" for the player.

A number of spells and bonus effects tend to have very undodgeable and unavoidable implementations, so despite the mod being interesting it makes a number of modifiers just unfair to go up against unless you specifically build to counter them or just flat out DPS/outheal race them. Which is not very fun and engaging.

Below is my hot take of all the effects and some suggestions to how they could be reworked.

1UP: Fair. When 1 up triggers, give them an extreme regen and resistance effect and trigger the totem effect. As I often remember the mob would not get their full health back, and only get their "base health" before infernal mobs would amplify it making them fall fairly quickly afterwards.

Alchemist: Fair enough, If you keep your distance. But potentially make the witch sound with particles from it's face before throwing the potion so you know it's coming?

Berserk: Fair.
Bulwark: Fair.
Cloaking: Fair. Hide infernal particle effects so they're actually invisible other than potion effects and skill triggers?
Lifesteal: Fair. +hearts particles when it heals off you?
Sprint: Fair. woosh sound effect when trigger?
Regen: Fair.
Ghastly: fair enough, if you're ready for it. Similar to alchemist, make a ghast noise a second before they throw the fireball?
Quicksand: Fair enough. it's just a slow. But consider making it only when they hit you. optional config toggle to allow shields to negate it.

Sapper: Fair enough. As the effect is sort of negated by just having food available. But consider making it only if they hit you. optional config toggle to allow shields to negate it.

Blastoff: Place a circle of smoke on the ground under the targetted player. Then after 1.5 seconds, make the particles accelerate into the air quickly throwing the player. Inspiration being wraiths and windcallers from minecraft dungeons (and by extension, dungeons mobs mod) where their AoE spells telegraph for a moment before erupting.

Choke: Require the mob to attack or be directly attacked by the player/mob and to maintain line of sight/aggro there after. If their aggro is switched by someone else attacking it, the effect switches target and breath returns. I recall previous versions also having a bug where after being choked your breath wouldn't restore properly for a while after, I hope thats fixed.
When being choked place a temporary potion effect similar to "accessible" mode nausea on the target (just visual), where the edges of the screen become greenish on the player.

Darkness: Affect player on direct hit. But sometimes the mob should become engulfed in smoke particles, before releasing a blast of smoke particles outwards blinding all nearby. If possibly, only blind the player if they have the mob on the screen. so you need to turn away to avoid being smoked.

Ender: When Ender is "charged" make the mob emit ender particles. No damage reflect to differentiate it to ninja. But teleport the mob closer to the attacking target and switch it's aggro to the triggering foe so it might attack them directly. Similar to an enderman running at you and teleporting as it goes.

Ninja: When ninja is charged make it emit smoke particles. On taking a hit, make it "avoid" the hit by becoming invulnerable and exploding in a puff of smoke before dropping an bomb that looks like a ninja replacement technique log. The log hits the ground then explodes about a second after in a small radius dealing the damage that was negated before the mob dodged. Ninja mob drops from the sky somewhere near the player with temporary resistance afterwards timed to be a little longer than the exploding log.

Fiery: Make the mob randomly catch fire but be immune to fire damage. While it's on fire, attacking the mob has a chance of catching you on fire briefly. The mobs attacks against you are gauranteed to catch you on fire. Mob can be extinguished or you can wait for it to not be ignited anymore to attack. Indirect attacks like bows and projectiles shouldn't catch the player on fire, allowing for counter play.

Gravity: Only within a certain distance of the player. Randomly produces bursts of ender particles that radiate outwards to knock player back. Or redstone particles which flow from a short distance away inwards. After this "telegraph" particle effects trigger the target of the mob if within direct line of sight to be pulled towards or pushed away from the mob.

Exhaust, Weakness, Poisonous, Wither: Only on being hit, or alternatively it can also be triggered through a successful hit of another spell, like the ninja log explosion, darkness burst, blast-off wave or through a mob owned projectile if the mob is such (like a skelly) etc.

Rust: It's kinda rude. But not much you can do except get naked and do big dps. :V As long as it only eats up the weapon being used, or the armor taking the hit on trigger. However an ability to re-balance it could be nice. Cause last I knew it was something silly like 30 durability a hit?

Sticky: A very unfair one, considering the amount of effort people go through to make items good nowadays in game. It's almost always turned off.
The only thing I can think of is to make the mob have slime particle effects if the effect is capable of triggering. Also make the item then "magnetize" or become stuck to the mob visually so it doesn't get thrown somewhere you don't want it to, like fire on the floor from lightning etc. Sorta like putting a display stand on the mobs head and attaching the item to it or something (tuff golem tech?)
To retrieve the item you hit the enemy a few times and the last item which was stuck from the specific player is retrieved back into the inventory. By being able to see the slime effects you can strike it with something you don't need immediately if you pay attention.

Storm: No u.
This is one is very strong and pretty unfair. Do a similar effect to blast off with a target point marked with particles, maybe enchanting particles, before striking lightning. Also I heard that you can stop it triggering by being under a shelter, but sometimes you just don't have that, and it's literally already killed you cause of lightnings high damage and being completely unaware to it until it's too late.

Vengeance: Make the mob glow red after sustaining a number of hits or a percentage of it's health in damage. After this triggers vengeance is active for 5 seconds where it always reflects damage before turning itself off again and being unable to reactivate for 10 seconds. or until it withstands a similar number of hits/damage which hastens the cooldown. This basically cuts the fight down into sections with a bit of reflecting rage sort of skill in between each loose health bar.

Webber: I think dungeon gear adds a mechanic where spiders spit silk blobs at you which web you down? maybe you could borrow something similar to that effect? the web ball is thrown by the mob periodically and it just webs under the mob/player it hits or just lays webs where it lands.

Finally:
Split the abilities into "passives", "reactive" and "active"/"thrown".
Reactive and active effects cannot be all active at once and should be cycled/postponed if another is already actively running. With enough effects it basically becomes semi-constant and a case of pick your poison and knowing your enemy based on tells you've seen previously and been a victim too (if you don't have visible effects on), but atleast you know what poison you're picking eventually. Rather than spontaneously catching fire while being withered, slowed and blind and then dropping your weapon in the struggle and having it vaporized by a lightning bolt while panicking and trying to run away. :V

Passive triggers can all be active at once, such as bulwark, 1 up, regen, sprints etc.
Active triggers like storm strikes, darkness bursts, lift-off waves or gravity pulses and maybe web shots, potion tosses and ghast fireballs should also only allowed to be triggered a short duration after one another. Either in a completely random cycle based on whats available and off cooldown or just in a cycle of what was applied to the mob first.

This is a huge, wall-of-text wishlist. To put it short, unless i have vacation and get incredibly bored and have literally nothing better to do (and my gaming backlog is considerable) this is very unlikely to happen by my hand.

I am however always open to pull requests wink wink

Welp, looks like most things are getting turned off for now, then. I'd love to try to actually help, but I'm only really good for ideas at this point. :<