Beast
Chromalisks
Besides the normal spit attack, they should be able to create a haze aura around them that delivers their corresponding status-type

Chromalisk Whelp
Instead of taking one item, take all 3. In T3 they should also take the player's vitapod.

Wolvers
Wolver bites should have a chance of triggering a "bleeding" status effect which makes the knight lose certain amounts of HP, on top of the status effect if applicable. Much like burning. Generic wolvers should have a very high chance of inflicting such a status.

Alpha Wolvers
Their 3 bites are overpowered, the damage is way too high right? Well, nerf it by making them invincible while performing the 3 bites. Alpha wolvers should also be able to heal other normal wolvers if any is around, they cannot heal themselves.

Construct
Gun Puppies
Make them invincible to normal gun shots from the front. Charges should still do damage. Not applied to rocket puppies.

Rocket Puppies
Homing missiles should have a chance to blast through the shield and also trigger a huge explosion. The size of a 3* Nitronome would do.

Red Rovers
Fire 3 streams of flames instead of one, also leave a temporarily flaming barrier left behind.

Love Puppies
Damage knights that are poisoned instead of doing nothing.
Have a chance to spit out a poisonous heart which damages the player and inflict a random status.

Mecha Knights
Fire 8 bullets instead of one while charging.
Have a chance to trigger an explosion upon death, deliver stun to the player.

Retrodes
Make them shoot lasers from time to time too, make them invincible while doing that brandish-like charge attack.

Scuttlebots
Give them another skill where they can become invisible and teleport behind the player.

Shufflebots
Chance to instant kill the player?

Fiend
Devilites
Give them some sort of AoE attack, like a DA charge with with a smaller field of cover. Firing 3 projectiles would also do the job
Make Pit Bosses invincible when there are other overtimers around
Yesman should be able to heal other devilites too

Gorgos
Bodyslam should be impossible to distract. Summon AOE spikes that damage the player

Greavers
Make them invincible while gliding
Haze should actually do something, the radius should be the size of a 3* mist bomb.

Trojans
Make them impervious to any bullet-type damage at low health. One blitz at the back is boring.

Silkwing
Fully heal the surrounding monsters upon death. Not applicable to boss-types and does nothing if the monster is poisoned.

Gremlins
Knockers
Attack more frequently

Slimes
Polyps
The spikes should be 360 degrees rather than the laughable barely-200 degrees

Undead
Phantoms
Make these spawn in LOA please.

Okay, you get it.
I'm asking to buff certain monsters that are way too easy to deal with. Gremlins are generally elite mobs and can be a pain from time to time, same with slimes and their annoying projectiles, although I think Lichens should fire up to 12 projectiles. I would love to see certain changes whenever that "Arcade Redux" comes out. There won't be a T4 anytime soon but these changes will definitely make PvE more enjoyable, at least in my opinion.