Good grief, this is pure torture!
Stunning pixel art paired with a character whose weak stats can't keep up. Hordes of agile enemies swarm you with ranged attacks, overwhelming a character who can only fight one foe at a time...
Perhaps much of your inspiration comes from Metal Slug, but in Metal Slug our primary attack method relies on various firearms far more powerful than other minor enemies. Melee combat requires various invincibility frames; otherwise, it simply doesn't work.
The health pool is far too low—just three bars. In the game environment, this is practically nonexistent. Swallowing enemies for healing yields very little, and as for the items in various crates... I barely survive long enough to see them drop.
The benefits of swallowing enemies are negligible. The lengthy swallow animation lacks invincibility frames, meaning swallowed enemies just get beaten to death by others.
Spitting out bones is a decent tactic, but could you add a group attack like spitting stomach acid? The characters' chubby builds would work perfectly.
For a pixel game, the gameplay is seriously lacking.