Various grounds for Metal Slug tiering.
Marco destroys helicopter
These helicopters should be no different from the real life helicopters like AH-64 Apache in durability.
They further destroy some tanks.
Marco & co eventually defeated some evil giants
The main characters defeated Evil Spirit Incarnate in Metal Slug 5.
Marco's height = 1.80 m = 37 px
ESI heart height here = 109 px = 1.8/37*109 = 5.302702703 cm
ESI heart height here = 106 px = 5.302702703 m
ESI as a whole = 908 px = 908/106*5.302702703 m = 45.42315145 m
Applying the Ugarik-Jasonsith giant model...
Tally - Evil Spirit Incarnate tiered by sheer size
Height = 45.42315145 m (Large Size Type 1)
Weight = 1216738.401 kg
Running speed = 171.2808858 m/s (Mach 0.499361183, Subsonic)
Combat speed = 264.3390049 m/s (Mach 0.770667653, Subsonic+) << At most Hypersonic by scaling to tank gun fires from main characters
Lifting strength = 34407574.34 kg (Class M)
Striking strength = 999479556.4 J = 0.238881347 ton TNT (Small Building level+)
Running energy = 17847813525 J = 4.26572981 ton TNT (Large Building level)
Since this beast should not be less tough than a mere M1 Abrams... yeah its AP and durability should scale to the total fragmentation energy of an M1 Abrams instead, with its combat speed scaling to hypersonic tank gun fires.