Final Fiesta II

Play through the entire game without shooting the dog.

911 Emergency

Shoot the dog at least once during the game. At hours 6 and 8, pick up the phone and press Q to call the police. Make sure to stay on the line for the duration of the call. Afterwards, shoot the dog at least once in the game world.

BackPack

Shoot the dog at least once during the game. Afterwards, initiate the final battle with him and do not let the TV get destroyed. Back in the real world you will now be able to shoot your gun. Keep an eye out for the dog as he has multiple entry points. Once you see him, shoot him until he dies.

Nuke the Game

Set your difficulty to normal (I don't believe the golden shells spawn on easy), then enter the game world. If you look at your ammo boxes you will see a shotgun shell that glows gold. Keep shooting until you load it into the gun where it will then turn gold itself. Aim down sight at the sun and shoot it. I was only able to activate the golden shells after a run where I won the final fight which is why I say to earn this ending now.

Broken Cartridge

Shoot the dog at least once. Afterwards, initiate the final battle with him and do not let the TV get destroyed. Back in the real world let the dog kill you.

TV

Shoot the dog at least once. Afterwards, initiate the final battle with him and let the TV get destroyed.

Dog

After earning the 6 other endings, load up a new game+ and play all the way through to the end without shooting the dog and earning the Fiesta ending again. After the final cutscene, you will be in the living room and will find a new VHS tape titled "It's Me" near the dog bed. Play it. After earning the Final Fiesta ending again, you will be teleported to the stage area. Go up on stage, and activate the music box by holding E and Q on the handle. Keep winding it until the stage opens up.

Mom!?

Simply pick up a highlighted object by pressing E, then hold E to charge up and toss it at your mother.

What Time is it?

This may be unlocked simply by focusing on the cat clock in the living room by holding right click while looking at it. Further confirmation would be nice!
I unlocked this during the dream phase where you need to wake yourself up by tossing an item towards the cat clock. Other people claimed they unlocked it during the final hour where you need to defend yourself against the dog.

Dinner Time

This can be a little finicky to unlock. During hour 5 you will see a stack of silverware on the table next to you. You must toss 2 plates, spoons, knives, and forks onto the table behind the couch and have them all stay on it at one time. I pressed up against the couch as much as I could and aimed at the light above me. Charge the shot about half way and hope the item lands. If you mess up, you can reload the hour by pressing 5 on the numpad.

Duck Champion

Shoot 100 ducks. This will more than likely unlock before you even finish your first playthrough.

Two Ducks One Shot

There will be many chances where 2 ducks line up for a single shot. It's almost impossible to miss this while going for all 7 endings.

Cat Tails

Shoot every last cattail while inside the game world. You can do this before or during the rounds. Some are a little tough to see so just keep looking around until the achievement unlocks!

Rabbit Season

While in the game world, walk up to the sign in front of you that says "duck season" and shoot it.

I'm Not Laughing

Simply shoot the dog twice.

Let's be Friends

Don't shoot the dog for an entire playthrough. This is required for one of the cartridge games as well as an ending. I suggest doing this on your first playthrough.

Cold Blooded

In the game world will be a passive duck sitting by your feet to the right. Simply shoot it like the monster you are.

Around the Globe

Pick up the globe by pressing E, then hold shift to inspect it.

You're a Wizard

The Kid Wizard book can be found on the bookshelf to the right of the TV. Most items it can be used on are locked until you earn the endings. The first item you can use it on is the action figure. Simply toss it at him and the achievement will unlock.

Scat Cat

Grab any highlighted item with E, then hold E to charge up your shot and toss the item out the window behind the TV.

Spooky

After earning all the endings, grab the Kid Wizard book and toss it at the computer behind the couch (where your mom sits at one point). You will be teleported into a secret room with every item in the game. Find the Kid Wizard book again and toss it at the giant pumpkin to be teleported into a zombie survival mini game. Keep killing zombies until the achievement unlocks.

1

Duck Season

Complete the game.

2

Duck Season

Complete the game without shooting the dog, then play and complete the Final Fiesta II cartridge.

3

Triple Tiger

To beat this, think of it as rock paper scissors going counter-clockwise. Round 1 and 2, look at the attack your opponent uses and use the next one over. Round 3, use the attack 2 over. Round 4, read his 3 attacks out, then use the counter 1 ahead of the move where his eyes glowed.

4

Ghouls

Slash the ghouls for 3 rounds. Easy peasy.

5

Hover Junkers

Spam the shoot button and the reload button at the same time for the whole game. Turns it into easy mode.

6

Whaling 1842

Don't spam your harpoons. Simply wait for the whale to breach, shoot it once, repeat. Do this for all the whales until you win.

7

Pizza Boy

This one can be a little annoying. You need to deliver all 15 pizzas to 2 neighborhoods, while not killing anymore than 3 people in the process. You can actually use the pizza toss to knock people out and avoid killing them.

8

Sinatra

Position your character just a little under the enemy models and spam the shoot button. You can damage them, but they can't damage you.

9

Battle Bros.

This game, in my opinion, is entirely luck based on whether you get a good enemy set up or not. The trick to winning is using every last electric box that makes you invincible.

1

Shotgun Tutorial

Plays automatically at the start of every new game.

2

Beach Justice!

Appears near the TV. Blue case.

3

Treasure Hunters

Appears near the TV.

4

Ode to GMod

Appears near the TV. White case.

5

Time Buddies

Appears near the TV.

6

Radical Racers

Appears near the TV.

7

There's no 'I' in Iowa

Appears near the TV.

8

Bootloose

Appears near the TV.

9

Kazoo Kid

Appears near the TV.

10

All Dogs go to Hell

Appeared near the TV after shooting the dog.

11

12

Appeared near the TV after shooting the dog. Transparent red and black case.