Every difficulty setting has unique unlockable rankings that may be unlocked depending on your performance throughout the game. Below are the possible unlockable rankings and the requirements to unlock them.

Ranking	How to unlock
Bat - Normal Difficulty	Tanker: 1 alert, Plant: 2 alerts, Tanker-Plant: 3 alerts.
Big Boss - Extreme Difficulty (Tanker-Plant)	Radar off, under 3hr clear, Damage: under 10.5, Shots Fired: under 700, under 3 alerts, 0 kills, 0 continues, 0 rations, 0-8 saves, no special items.
Capybara - Normal Difficulty	Tanker: 5+ hours, Plant: 25+ Hours, Tanker-Plant: 30+ Hours.
Cat - Very Easy/Easy Difficulty	Tanker: 25+ saves, Plant: 75+ saves, Tanker-Plant: 100 + saves.
Chicken - Very Easy/Easy Difficulty	Radar: off, 250+ alerts, 250+ kills, 60+ continues, 31+ rations used, 100+ saves.
Cow - All Difficulty Levels	Tanker: 50+ Alerts, Plant: 200+ alerts, Tanker-Plant: 250+ alerts.
Deer - Normal Difficulty	Tanker: 25+ saves, Plant: 75+ saves, Tanker-Plant: 100 + saves.
Doberman - Hard Difficulty (Tanker-Plant)	Under 3hr clear, under 3 alerts, 0 kills, 0 escapes, 0 continues, 0-3 rations, no special items.
Doberman - Normal Difficulty (Tanker-Plant)	Radar off, under 3hr clear, Damage: under 10.5, Shots Fired: under 700, under 3 alerts, 0 kills, 0 continues, 0 rations, 0-8 saves, no special items.
Eagle - Extreme Difficulty	Tanker: 18 minutes or less, Plant: 2hrs 45 min or less, Tanker-Plant: 3hrs or less.
Elephant - Normal Difficulty	31 Rations used.
Falcon - Normal Difficulty	Tanker: 18 minutes or less, Plant: 2hrs 45 min or less, Tanker-Plant: 3hrs or less.
Flying Fox - Hard Difficulty	Tanker: 1 alert, Plant: 2 alerts, Tanker-Plant: 3 alerts.
Flying Squirrel - Very Easy/Easy Difficulty	Tanker: 1 alert, Plant: 2 alerts, Tanker-Plant: 3 alerts.
Fox - Extreme Difficulty (Tanker-Plant)	Under 3hr clear, under 3 alerts, 0 kills, 0 escapes, 0 continues, 0-3 rations, no special items.
Fox - Hard Difficulty (Tanker-Plant)	Radar off, under 3hr clear, Damage: under 10.5, Shots Fired: under 700, under 3 alerts, 0 kills, 0 continues, 0 rations, 0-8 saves, no special items.
Gazelle - All Difficulty Levels	Tanker: 50+ Clearing Escapes, Plant: 100+ clearing escapes, Tanker-Plant: 150+ Clearing Escapes.
Giant Panda - Extreme Difficulty	Tanker: 5+ hours, Plant: 25+ Hours, Tanker-Plant: 30+ Hours.
Hawk - Hard Difficulty	Tanker: 18 minutes or less, Plant: 2hrs 45 min or less, Tanker-Plant: 3hrs or less.
Hippopotamus - Extreme Difficulty	Tanker: 25+ saves, Plant: 75+ saves, Tanker-Plant: 100 + saves.
Hound - Easy Difficulty (Tanker-Plant)	Radar off, under 3hr clear, Damage: under 10.5, Shots Fired: under 700, under 3 alerts, 0 kills, 0 continues, 0 rations, 0-8 saves, no special items.
Hound - Normal Difficulty (Tanker-Plant)	Under 3hr clear, under 3 alerts, 0 kills, 0 escapes, 0 continues, 0-3 rations, no special items.
Jaws - Hard Difficulty	Tanker: 50+ Enemies killed, Plant: 200+ Enemies killed, Tanker-Plant: 250+ Enemies killed.
Koala - Very Easy/Easy Difficulty	Tanker: 5+ hours, Plant: 25+ Hours, Tanker-Plant: 30+ Hours.
Mammoth - Hard Difficulty	31 Rations used.
Mouse - Normal Difficulty	Radar: off, 250+ alerts, 250+ kills, 60+ continues, 31+ rations used, 100+ saves.
Night Owl - Extreme Difficulty	Tanker: 1 alert, Plant: 2 alerts, Tanker-Plant: 3 alerts.
Orca - Extreme Difficulty	Tanker: 50+ Enemies killed, Plant: 200+ Enemies killed, Tanker-Plant: 250+ Enemies killed.
Ostrich - Extreme Difficulty	Radar: off, 250+ alerts, 250+ kills, 60+ continues, 31+ rations used, 100+ saves.
Pig - Very Easy/Easy Difficulty	31 Rations used.
Pigeon - All Difficulty Levels	No Enemies Killed.
Piranha - Very Easy/Easy Difficulty	Tanker: 50+ Enemies killed, Plant: 200+ Enemies killed, Tanker-Plant: 250+ Enemies killed.
Rabbit - Hard Difficulty	Radar: off, 250+ alerts, 250+ kills, 60+ continues, 31+ rations used, 100+ saves.
Sea Louce - All Difficulty Levels	Beat the game with a Sea Louce in your inventory.
Shark - Normal Difficulty	Tanker: 50+ Enemies killed, Plant: 200+ Enemies killed, Tanker-Plant: 250+ Enemies killed.
Sloth - Hard Difficulty	Tanker: 5+ hours, Plant: 25+ Hours, Tanker-Plant: 30+ Hours.
Swallow - Very Easy/Easy Difficulty	Tanker: 18 minutes or less, Plant: 2hrs 45 min or less, 3hrs or less.
Whale - Extreme Difficulty	31 Rations used.
Zebra - Hard Difficulty	Tanker: 25+ saves, Plant: 75+ saves, Tanker-Plant: 100 + saves.