Potion effects system

Potions aren't very used by players...sure, they can be useful, but many effects are not usually thought to be necessary, mainly beacause they don't really give that many benefits

I would propose a couple of changes, to make potions a bit more worth using

Potion vulnerability

Certain enemies will be more vulnerable or immune to certain potion effects, like undeads take damage from Instant Health and are healed by Harming, and how spiders are immune to poison. Here's a few additions and changes

• Undead: weakened by Strenght and strenghten by Weakness (however to cure a zombie villager it wouls till require a weakness potion), slowed by Speed and sped up by Slowness
• Fire mobs (magma cubes, blazes and striders) take damage from Fire Resistance potions
• Ender mobs take 50% more damage from Poison
• Living mobs take 50% more damage from Wither
• Ice Mobs (snow golems, polar bears and strays) are resistance to Slowness and Weakness

Poison buff

As long as we have the Poison effect, the timer of the effects of Blindness, Weakness, Slowness and Nausea won't go down

Weakness buff

Each level of weakness reduces by 20% the natural healing speed, capped at 80%

Wither buff

Withered mobs won't regenerate health naturally as long as they have the Wither effect

Slow Falling

Slow Falling nullifies Ender Pearl damage