Champions Arise

nfestation:  On death, silverfish will spawn, and the attacker will get the infestation effect.

Poison: Adds the poison effect to the attacked player, with a random duration and intensity.

Blindness: Gives the blindness effect to its target

Leaping: The mob will jump around in the direction of its target.

Magnetism: Nearby players get pulled in the direction of the mob.

Breezing: Shoots wind charges at its target.

Blizzard: Shoots freeze charges that slow down its targets.

Thrust: Launches the attacked entity into the air.

Cleaving: When defeated, the mob will spawn copies of itself.

Healing: The mob heals other monsters around it, but not itself!

Dominion: Massive increase on speed and health.

Harming: On death, nearby monsters will receive a big amount of damage.

Iron: The mob becomes slower, but has a massive health boost and slows down its targets

Invisibility: The mob is invisible.

Striking: The mob deals lightning damage and sets targets on fire.

Freezing: When attacking an entity, the attacked entity will get slowness at a random duration and intensity.

Scorching: Will set the attacked entity on fire.

Rising: The victim gets the levitation effect for a random duration and intensity.

Decay: Gives the wither effect when attacking.

Vitality: Has a massive health boost

Champion Key

Effect: Can be used to open Vaults in the Champions Tower.

How to obtain: Obtained as a reward from the spawners inside the Champions Tower.

Ominous Champion Key

Effect: Can be used to open Ominous Vaults in the Champions Tower.

How to obtain: Obtained as a reward from the spawners inside the Champions Tower while under the Trial Omen effect.

Shulker Fruit

Effect: When eaten, the player will get a Levitation and Slow Falling effect, quickly making the player ascend and descend safely. Ideal for climbing or escaping mobs.

How to obtain: Can be dropped as a reward from some Champion Mobs, but can also be found as loot in the Champions Tower.

Freeze Charge

Effect: When used, a freezing projectile will be shot, when it hits an entity or block, it will slow them down for a couple of seconds.

How to obtain: Can be dropped as a reward from some Champion Mobs, but can also be found as loot in the Champions Tower.

Electric Charge

Effect: When used, an electric projectile will be shot, and when it hits an entity or block, it will summon a lightning bolt, as well as dealing +12 damage to the hit entity.

How to obtain: Can be dropped as a reward from some Champion Mobs, but can also be found as loot in the Champions Tower.

Mystic Apple

Effect: When eaten, the player will heal 2 hearts or 4 hp.

How to obtain: Can be dropped as a reward from some Champion Mobs, but is mainly found as loot in the Champions Tower.

Contained Heart

Effect: When used, the player will be fully healed and gain an additional 10 hearts of health for 10:00 minutes.

How to obtain: Can be dropped as a reward from some Champion Mobs, but is mainly found as loot in the Champions Tower.

Contained Golden Heart

Effect: When used, the player will be fully healed and gain Absorption IV for 10:00 minutes.

How to obtain: Can be dropped as a reward from some Champion Mobs, but is mainly found as loot in the Champions Tower.

Trial Omen Potion

Effect: When consumed, the player will get the Trial Omen effect for 60:00 minutes. Since to get it through Bad Omen requires you to go to a Trial Chamber, this is an easier way to get it and use the effect in the Champions Tower

How to obtain: Can be dropped as a reward from the spawners in the Champions Tower.

Champion's Curse Potion

Effect: When consumed, the player will get the Champion's Curse effect, which causes all enemies around the player to spawn as Champion variants as long as the effect lasts. This can be used to challenge yourself and get more rewards, or event to maximize the effectiveness of mob farms. 

How to obtain: Can be dropped as a reward from the spawners in the Champions Tower.

Note: This effect can be removed by drinking milk.

Vanishing Potion

Effect: When consumed, the player will get the Vanishing effect, which makes the chance of a Champion variant spawning virtually zero as long as the effect lasts. If this potion is used at the same time as a Champion's Curse potion, the effects of both will "negate" and the chance of Champions spawning the will be set at 50%, as long as both effects are had.

How to obtain: Can be dropped as a reward from the spawners in the Champions Tower.

Note: This effect can be removed by drinking milk. Additionally, if this potion is used inside a Champions Tower under the Trial Omen effect, the chance will only be lowered instead of nullified.

Champions Ring (Broken)

Effect: Has no effect in this state. Can be repaired by using 3 diamonds to craft it into a fixed state.

How to obtain: Can be dropped as a reward from the Ominous Vaults in the Champions Tower.

Champions Ring 

Effect: When this item is in the player's inventory, the player will gain a Speed I effect, along with a 50% damage increase to all attacks. In exchange, ALL mobs will spawn as champions as long as this item is carried. If a player attacks an entity while having this item, the ring will take damage, having a durability of 600. Once the durability runs out, the ring will become broken again.

How to obtain: Has to be crafted from a broken ring.

Notes:

The damage increase is not done through the Strength potion effect, meaning it can also stack with it.

If this item is used along with a Potion of Vanishing, the result will be the same as using Vanishing and Champion's Curse at the same time, meaning, the chance of champion mobs spawning will be 50%.

Quick Bow

Effect: Functions like a normal bow, but charges much faster, additionally, the player is NOT slowed down while using it, meaning it can be charged and held while sprinting. However, this bow cannot use tipped arrows.

Enchantments: All bow enchantments

How to obtain:  Can be dropped as a reward from the Ominous Vaults in the Champions Tower.

Assault Hammer

Effect: A melee weapon that at base deals 8 points of damage, but can throw enemies into the air when hitting them. The thrust inflicted varies depending on the velocity the user has, meaning attacking something while falling causes it to get thrown higher in the air. However, this weapon has a light cooldown when attacking, meaning if you want to get your enemy constantly in the air, you will have to time it correctly.

This weapon also has a chance of dealing critical attacks,  which cause the target to get slowness for a brief period as well as getting thrown way higher into the air.

Enchantments: This weapon uses pickaxe enchantments, meaning efficiency, fortune, and silk touch, but do NOT be fooled, this is not a pickaxe, and these enchantments have a very different effect:

Efficiency: Increases the damage dealt by the weapon by +1 each level.

Silk Touch: Reduces the weapon cooldown considerably

Fortune: Increases the thrust of the weapon, as well as increasing the chance of a critical attack with each level.

How to obtain:  Can be dropped as a reward from the Ominous Vaults in the Champions Tower.

Hyper Enchanted Book

Effect: When used, it will summon a hyper enchanted item and give it to the player. This means the player can get all sorts of weird enchantments such as a pickaxe with Efficiency VI, a chest plate with Protection V, a sword with Sharpness VI, among others.

How to obtain:  Can be dropped as a reward from both Ominous Vaults and Regular Vaults in the Champions Tower.

Detached

A new type of zombie that is slightly faster, and when defeated, will split into a head and a body that will both attack targets. The body attacks through melee, while the head will shoot fire projectiles.

Necrohowler

An undead mob that is slightly faster than other undead mobs and attacks through melee, however, if you look at in the "eye", it will give you the Slowness and Blindness effects, so be careful where you look.

Scarecrow

A simple mob that is very fast, but not very strong. Will hunt and attack players through melee attacks, and it might catch you by surprise, but the attacks are not that strong, and their health is not that much stronger either.

Revenant

A ranged attack mob that will shoot fire projectiles that deal a good amount of damage. However, their health is lower than most hostile mobs, so try to take them out fast.

Bisectoid

This, thing, is a very aggressive, very fast, and very strong undead mob. Be very careful around them and act quickly, since they will not allow you to take a breath.

The Forgotten

The new boss this Add-On brings. It has all sorts of attacks, going from sworded, ranged, wind charges, maces, and can even use the brand-new Assault Hammer. It has a good amount of health and will drop a good amount of XP, as well as having a very high chance of spawning as a Champion variant, so be prepared for a good fight. 

Note: It has no unique drop, its purpose is to guard the Vaults found in the Champions Tower

There are more mobs added with this Add-On, but the rest are just slight variations of existing mobs, so its not necessary to cover them here.