Story-related; You need to increase your Deersaster level in the first area to "A". Do this by destroying cars, trees, buildings etc. and dealing with the police that come after you. Once you reach Deersaster level "A", the DOGGO boss will spawn in.
Use your guns and other weapons to shoot its legs and knock it down. Then shoot the police cars on its shoulders to reveal large red buttons. Finally jump up and hit those buttons then finish the DOGGO off with more gunfire. The Metal Deer from Kept You Waiting? (70G) is super helpful here.
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 Achievement11:55 - 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