DEEEER Simulator: Your Average Everyday Deer Game

Once you die 3 times to the boss fight with your future self and curse of the deer, you get another heart next try so you'll have 4. Die a fourth time and you'll have 5 hearts. What worked for me was to only use melee and follow them around swinging not worrying about damage.

After this is a QTE rock, paper, scissors. Press when he winds back with a strong attack. Press when he stretches his neck with a quick attack. Press when he puts up his barrier.

Choose Don't Fire. You'll have are harder boss battle, but you can use the heart trick again to make it easy. I don't think you need to fire, you just have to dodge attacks to progress.

After the fight with the curse of the deer choose not to fire - fight another boss and the achievement will pop.

If you are interested in a very fast guide :


Timestamps:

00:00 Intro + Self-sacrifice Achievement
00:59 Story Present + Town Musician of Bremen Achievement
04:08 Story Future Ending 1 + 13th Deer Achievement
07:23 Story Future Ending 2 + The Trudeer Show Achievement
08:49 Counting Sheep, Deer-hunting Achievements
09:18 Dead or Deer Achievement
09:33 God Disguised as a Cow, Kept you Waiting? Achievements
10:19 100% BEEF Achievement
10:47 Like a Truck, Dunkleosteus Achievements
11:20 The Devine Move Achievement
12:30 Genius Achievement
13:19 Rhinosaber Achievement
13:49 Big Time monkey. I am Deeeer Achievements

After beating the boss battles in stage 2 you have 2 options to choose from. Choose "Don't Fire"
You'll then do another battle where you need to survive
You'll unlock the dragon ride/weapon after

1:40 Hit By Truck
2:15 Deerify 10 Humans
2:30/13:35 30 Guns
3:45/ 14:20 100 Sheep
6:45 Ride the cow
7:20 Ride Metal Deer
8:10 Doggo Boss
17:50 True Ending
27:50 Giant Koala
28:10 Giant Fish
28:30 4 Burgers
29:00 Cowthello
31:25 Animal Puzzle
33:05 Big Time Monkey
33:35 Defeat Rhinos
36:15 Average Ending

Achievement Walkthrough:

After defeating your Future Self, you'll be given a choice. You should choose "Don't Fire" to not shoot your Future Self. You will need to complete another, much more difficult boss fight, then this will pop during the credits.


Timestamps:
00:00 - Intro
00:20 - Self Sacrifice Achievement
00:48 - Dead or Deer Achievement(Start)
01:00 - Deer Hunting Achievement (Start)
02:05 - Counting Sheep Achievement (Start)
02:46 - Dead or Deer Achievement (Unlock)
05:36 - God Disguised as a Cow Achievement
06:15 - Kept You Waiting? Achievement
09:00 - Town Musicians of Bremen Achievement
11:55 - Deer Hunting / Counting Sheep Achievement (Continued)
15:15 - Counting Sheep Achievement (Unlocked)
15:50 - Deer Hunting Achievement (Unlocked)
19:50 - Final Boss Fight
23:10 - The Trudeer Show Achievement
26:10 - Like A Truck Achievement
26:50 - Dunkleosteus Achievement
27:10 - 100% Beef Achievement
27:40 - The Divine Move Achievement
29:05 - Genius Achievement
31:20 - Big Time Monkey Achievement
32:28 - Rhinosaber Achievement
33:23 - 13th Deer & I Am DEEEER Achievement