The problem is if an alert is set off, like big boss camo sends off an initial alert then it fades as the guards run in fear of your dead face, I don't know about corpse I don't have it. I did the Big Boss Emblem with the Mk.2 using emotion rounds at times where useful and the normal when vital, and just abused Facecamo and octocamo where I could. No real special tricks, just avoiding combat is the way really.
No real spoilers inside, so here they are. Getting all 40 gives you some rewards, I don't know what but it's nothing significant. Getting the Big Boss Emblem gets you alot of others at the same time, well worth it.
1. Big Boss
Type: Elite
Difficulty: 10/10
Criteria
Number of Alert Phases: 0
Number of kills: 0
Number of continues: 0
Game time: < 5:00
Rations, Regain, Noodles used: 0
*No use of Stealth Camouflage or the Bandana
*The Boss Extreme
Special Completion Bonuses: Patriot, Big Boss FaceCamo, Big Boss iPod song.
2. Fox Hound
Type: Elite
Difficulty: 9/10
Criteria
Number of Alert Phases: < 3
Number of kills: 0
Number of continues: 0
Game time: < 5:30
Rations, Regain, Noodles used: 0
*No use of Stealth Camouflage or the Bandana
*Big Boss Hard or higher
Special Completion Bonuses: Thor .45-70
3. Fox
Type: Elite
Difficulty: 8/10
Criteria
Number of Alert Phases: < 5
Number of kills: 0
Number of continues: 0
Game time: < 6:00
Rations, Regain, Noodles used: 0
*No use of Stealth Camouflage or the Bandana
*Solid Normal or higher.
Special Completion Bonuses: Desert Eagle (Long Barrel)
4. Hound
Type: Elite
Difficulty: 7/10
Criteria
Number of Alert Phases: < 3
Number of kills: 0
Number of continues: 0
Game time: < 6:30
Rations, Regain, Noodles used: 0
*No use of Stealth Camouflage or the Bandana
*Naked Normal or higher.
Special Completion Bonuses: Type 17 Pistol
5. Mantis
Type: Elite
Difficulty: 8/10
Criteria
Number of Alert Phases: 0
Number of kills: 0
Number of continues: 0
Game time: < 5:00
Rations, Regain, Noodles used: 0
6. Wolf
Type: Elite
Difficulty: 5/10
Criteria
Number of continues: 0
Rations, Regain, Noodles used: 0
7. Raven
Type: Elite
Difficulty: 4/10
Criteria
Game time: < 5:00
8. Octopus
Type: Elite
Difficulty: 6/10
Criteria
Complete MGS4 with 0 Alert Phases
Special Completion Bonus: Stealth Camouflage
9. Bear
Type: Unique
Difficulty: 5/10 (1/10 with Stealth Camouflage)
Criteria
Defeat 100 or more enemies with CQC chokeholds.
10. Eagle
Type: Unique
Difficulty: 3/10
Criteria
Perform 150 headshots or more.
11. Assassin
Type: Unique
Difficulty: 5/10 (1/10 with Stealth Camouflage)
Criteria
Enemies defeated with knife kills or knife stuns >= 50
Number of CQC holds >= 50
Number of times discovered <= 25
Special Completion Bonus: Altair Disguise
12. Pigeon
Type: Unique
Difficulty: 5/10
Criteria
Number of kills: 0
Special Completion Bonus: Bandana
13. Blue Bird
Type: Unique
Difficulty: 3/10
Criteria
Number of items given to militia/rebels >= 50
14. Hawk
Type: Unique
Difficulty: 3/10
Criteria
Number of times praised by militia >= 25
15. Little Gray
Type: Unique
Difficulty: 6/10 (10/10 if you don't use Extras menu passwords.)
Criteria
Acquire 69 unique weapon types (excluding 1911), or 70 (including 1911).
16. Ant
Type: Unique
Difficulty: 6/10 (2/10 with Stealth Camouflage)
Criteria
Perform 50 or more body searches during hold-ups.
17. Gibbon
Type: Unique
Difficulty: 5/10 (2/10 with Stealth Camouflage)
Criteria
Perform 50 or more hold-ups.
18. Tortoise
Type: Unique
Difficulty: 3/10
Criteria
Spend more than 60 minutes hidden inside the Drum Can or Cardboard Box.
19. Rabbit
Type: Unique
Difficulty: 1/10
Criteria
Turn the pages of Playboy or the Emotion Mag 100 times or more.
20. Bee
Type: Unique
Difficulty: 4/10
Criteria
Scan or inject PMC soldiers with Scanning Plug or Syringe respectively on 50 occasions or more.
21. Gecko
Type: Unique
Difficulty: 2/10
Criteria
Spend 1:00 hour or more clinging to a wall.
22. Scarab
Type: Unique
Difficulty: 1/10
Criteria
Perform over 100 rolls.
23. Frog
Type: Unique
Difficulty: 1/10
Criteria
Roll or jump to the side 200 times or more.
24. Inch Worm
Type: Unique
Difficulty: 2/10
Criteria
Crawl for 60 minutes or more.
25. Lobster
Type: Unique
Difficulty: 3/10
Criteria
Crouch for 2:30 hours or more.
26. Hyena
Type: Unique
Difficulty: 1/10
Criteria
Pick up 400 weapons/items or more.
27. Hog
Type: Unique
Difficulty: 3/10
Criteria
Enter a Combat High 10 times or more.
28. Pig
Type: Unique
Difficulty: 2/10
Criteria
Use 40 or more Rations, Noodles or Regains.
29. Cow
Type: Unique
Difficulty: 1/10
Criteria
Number of Alert Phases: > 100
30. Crocodile
Type: Unique
Difficulty: 2/10
Criteria
Number of kills: >= 400
31. Giant Panda
Type: Unique
Difficulty: 1/10
Criteria
Game time: >= 30:00
32. Scorpion
Type: Common
Difficulty: 3/10
Criteria
Number of Alert Phases: <= 75
Number of kills: <= 250
Number of continues: <= 25
33. Tarantula
Type: Common
Difficulty: 2/10
Criteria
Number of Alert Phases: <= 75
Number of kills: > 250
Number of continues: <= 25
34. Centipede
Type: Common
Difficulty: 1/10
Criteria
Number of Alert Phases: <= 75
Number of kills: <= 250
Number of continues: > 25
Special Completion Bonus: Though there are no rewards for specific to the rating, you'll get the Corpse Camo in the (rather unlikely) event that your total continues exceed 41.
35. Spider
Type: Common
Difficulty: 1/10
Criteria
Number of Alert Phases: <= 75
Number of kills: > 250
Number of continues: > 25
Special Completion Bonus: Though there are no rewards for specific to the rating, you'll get the Corpse Camo in the (rather unlikely) event that your total continues exceed 41.
36. Jaguar
Type: Common
Difficulty: 2/10
Criteria
Number of Alert Phases: > 75
Number of kills: <= 250
Number of continues: <= 25
37. Panther
Type: Common
Difficulty: 2/10
Criteria
Number of Alert Phases: > 75
Number of kills: > 250
Number of continues: <= 25
38. Leopard
Type: Common
Difficulty: 2/10
Criteria
Number of Alert Phases: > 75
Number of kills: <= 250
Number of continues: > 25
Special Completion Bonus: Though there are no rewards for specific to the rating, you'll get the Corpse Camo in the (rather unlikely) event that your total continues exceed 41.
39. Puma
Type: Common
Difficulty: 1/10
Criteria
Number of Alert Phases: > 75
Number of kills: > 250
Number of continues: > 25
Special Completion Bonus: Though there are no rewards for specific to the rating, you'll get the Corpse Camo in the (rather unlikely) event that your total continues exceed 41.
40. Chicken
Type: Joke
Difficulty: 2/10
Criteria
Number of Alert Phases: >= 150
Number of kills: >= 500
Number of continues: >= 50
Game time: >= 35:00
Number of uses of life restoring items: >= 50