Here is the full list of all 19 Mechstermination Force achievements.
Defeat Mechtorial 01
Defeat Mechapede S82
Defeat Mechstructor ZC
Defeat Mechscargot ZR
Defeat MechaMan X3
Defeat Mechbeth L2M
Defeat GunMech Five
Defeat Mechemoth Z7
Defeat Mechrachnid W6
Defeat MechGyver C3
Defeat CerberMech DX
Defeat Mechtastrophy S5
Defeat TriMechalon 2000
Defeat the Mega Duck
Beat the game in less than 30 minutes
Get the No Damage bonus on each MegaMech
Beat the game without dying
Get a ★★★ rating on each MegaMech
Find love