Here is the full list of all 15 The Otterman Empire achievements.
Eliminations with All Charatcers - 100 Eliminations
Shots fired with All Characters -10000 Shots
Hitting Enemies with All Characters - 5000 Hits
Be Otterly devoted and play for 100 hours at least
Turret Eliminations with All Characters - 500 Turret Eliminations
Drone Eliminations with All Characters - 1000 Drone Eliminations
Tank Eliminations with All Characters - 100 Tank Eliminations
Bombs Dunked through Hoops with All Characters - 200 Bombs Dunked
Detonator Held with All Characters - 1 Hour Detonator Held Time
King of the Kill capture time with All Characters - 1 Hour King of the Hill Held Time
Robots Repaired with All Characters - 100 Robots Repaired
Hoop Lasers Destroyed with All Characters - 300 Laser Hoops Destroyed
Bombers Eliminated with All Characters - 100 Bomber Eliminations
Targets Returned will All Characters - 500 Targets Returned
Battery Banker Powered with All Characters - 100 Battery Bankers Powered