This is a guide on how to unlock all achievements in The Two of Us. Some things to know before you play is that the sword frog kills enemies in 2 hits while the shuriken frog kills in 3-4. The last thing is that the achievements Hard Carry and Pacifist will only be given to the host even if the other player meets the requirements.

1. It Takes Two: Pretty sure you just get into a lobby with a friend.
2. First Level Completed: Complete the first level.
3. Killer: Kill your first enemy.
4. Lemming: Die 5 times.
5. Pacifist: For this one have your friend play the shuriken frog and let them kill all the enemies while you kill none. Even though the shuriken frog takes longer to kill its better for this because its attacks are ranged.
6. Hard Carry: You play as the shuriken frog and kill all the enemies. Just do the opposite of what you did for the Pacifist achievement.

Two hidden achievements
7. Unkillable: Don't die. This achievement is easiest to get along with the Speedrunner achievement.
8. Speedrunner: Beat the game in under 5 minutes.

New achievements and how to unlock them:
9. Mass Killer: Kill 20 enemies
10. Stage 1 Completed: Complete all of stage 1.
11. Stage 2 Completed: Complete all of stage 2.
12. Game Completed: Complete all of stage 1 and 2.
13. Speedrunner Stage 2: Complete all of stage 2 in under 3 minutes.
14. Speedrunner: Unlock both the Speedrunner Stage 1 and 2 achievements.

Videos:
Use this video as a guide on how to beat stage 1 in under 5 minutes.
https://www.speedrun.com/the_two_of_us/run/ywjk480z
The sword wall bypass has been patched but the video will still help and the achievement is still obtainable.
Use this video as a guide on how to beat stage 2 in under 3 minutes.
https://www.speedrun.com/the_two_of_us/run/y9ld5nry
I did not make either of these videos.