Overview

Each boss has a specific requirement for pacification. All of these so far include not hitting the boss for a certain amount of time. For brevity, I will simply write in a minute amount per entry, such as:

Big Boss: 1 minute, don't kill his friends.

Similarly, most bosses can only be pacified once.

Bosses

Prehardmode

Vanilla

King Slime:

Hitting the boss makes it impossible to pacify.

If you do not hit him, and after 15 seconds, he'll start spawning projectiles alongside his normal AI.

Each time he does this, he gets a little smaller. Eventually, he'll be so small he gives up, and is pacified.

Eye of Cthulhu:

The big Eye is irritated! Some water will help him calm down.

After dipping him in water 5 times, he'll relax, and be pacified.

Eater of Worlds:

Before you fight him, collect some Rotten Flesh. Get a lot of it - at or over 30.

With this, you can craft Worm Morsels; small, gross little treats for the Eater to...eat. To feed it, throw the morsels at it. Just at any part of it's body. 30 of them will satisfy it, though note - it'll spit out additional Devourers as it eats!

Oh, and if you directly feed it's head, it's twice as effective. It'll only need 15 morsels if you feed its head directly.

Brain of Cthulhu: When spawned, the Brain will spawn a ton of fleshy spikes along all walls.

Creepers will grab these spikes, and if they touch the Brain, slowly put it to sleep.

These spikes also do a lot of damage, so be careful!

Deerclops: There's one thing Deerclops loves - breaking things!

Putting hay, [wo]mannequins and target dummies in her way will make her break through them.

She loves to break [wo]mannequins much more than hay.

Putting enough of these in front of her will eventually calm her down.

Queen Bee: Queen Bee has dreamed of a specific home ever since she was a larvae.

Naturally spawned Larvae will have various items on top of it. These items are all required items to place in her new home, so obtain them, make a nice looking home with all of them in there, and double-check that it's a valid house.

Then, break open the larva, and walk into the house. At this point, the Queen will take a moment to see if you've done everything right, and if you did - congrats!

Otherwise, you'll have to try again with a different Queen.

Skeletron: Skeletron will spawn various lanterns near his spawn location.

You have to light these lanterns in order, which may be difficult as they are sometimes a way up above the ground.

Once that is done, his curse is lifted, and you have a large bony friend.

Wall of Flesh: Talk to the guide at any point after beating the evil boss.

He'll talk to you offering help and give you a Guide's Locket.

This can be used to summon a more difficult version of the Wall of Flesh, which spawns additional leech enemies.

Transparent varieties of these enemies will be differently colored, and should be touched in order to return them to the Wall and pacify it slowly. These leeches, transparent or not, explode after a few seconds.

Hardmode

Queen Slime: 2 minutes, in first phase.

Destroyer, The Twins, and Skeletron Prime: A couple of steps.

First, craft at least 12 Cobalt or Palladium Orbs, a new item that functions similar to a grenade.

Then, spawn the boss. Throwing these Orbs at the boss will shock it, making it gain some random amount of speed and damage, with a short cooldown.

Repeat 12 times or more and the boss will eventually short-circuit and be pacified.

Plantera:

Every few seconds during her fight, she'll spit out a small flower bulb, which, upon landing, does one of four things.

White Flower / Lily - Spits out small petal projectiles, aiming at Plantera.

Red Flower / Rose - Creates an aura of attraction, drawing the player closer.

Blue Flower / Poppy - Fades quickly.

Blue Flower / Black Poppy - Fades to black, then explodes.

All of these flowers, when touched, "heal" some part of Plantera. Eventually, she'll be pacified.

Golem:

In ONE random Lihzahrd chest, you will find a Lihzahrd Power Brick.

This brick can be used, throwing it forward then returning when letting go. This does nothing to every NPC except one,

Golem. Hitting any part of Golem with it will shock it, increasing its behaviour speed but creeping slower towards pacification each time.

So, what you have to do is:

Hit Golem's head 5 times, immediately detaching it from the body. Then, hit it 5 more times, at which point it will break, powering down uselessly.

BEFORE beating Golem, use an additional Lihzahrd Power Cell on Golem's head to restart it, pacifying it. The body will continue to aggro.

At this point, Golem's body must be hit 20 times before it completely malfunctions, exploding and beating the boss. Killing the boss normally in this state after pacifying the head is also an option, though much slower. Just note that Golem's body gets SIGNIFICANTLY faster and will be very difficult to deal with.

Duke Fishron:

First, make sure you have a Bug Net handy.

Spawn him normally, but wait for him to spawn his Sharknados.

Now, the sharknados will occasionally have Truffle Leeches spinning around them. These leeches will latch on to you, inflicting both bleeding and poisoned for the duration of their time sucking your blood.

However, with a bit of skill, you can catch these leeches. 20 of them craft The True Truffle Treat, widely known to be a Fishron's delicacy of choice. Throw this out while fighting Fishron and he'll immediately aim for it. Eating the True Truffle Treat will pacify him instantly.

Empress of Light:

Before summoning her, craft a Prism Lens. This lens can be used to siphon her light, slowly depleting her strength.

After summoning her, hold the Prism Lens and you will see the light leave her. That light will modify your movement, however, making it much harder to dodge.

After harnessing enough of her light, she will let you live. For now.

Lunatic Cultist:

Fight him normally. After a while, he'll spawn a summoning circle with a few clones - ignore them, and move to the center of the circle.

After a short delay, the circle will be interrupted, and he will become enraged. A completely different fight begins here.

The pacification occurs when you are close enough to him; the closer, the faster.

Enemies

Pinky: Give it a Lesser or normal Healing Potion, or any food item.

Nymph: Throw Purification powder on her.

Tim:

He will spawn with three runes around him.

They are tethered to him; the tethers will do damage and hurt you.

Touching a rune will disrupt it; do this for every rune and he'll be pacified.

Skeleton Miner: Give them a Gold or Platinum Bar.

Surface, Gold or Shadow Mimic: Place a Chest Mimic next to them, open and close the Chest Mimic repeatedly. Do not alert them by moving too quickly.