Cube
At exactly five feet in height this cube of gelatinous ooze might not seem overly big, until one realizes it is indeed a cube, both five feet wide, and five feet deep.  Significantly heavier than any humanoid that takes up an even remotely similar space Cube does just fine on most surfaces because his weight distribution is so even, but things like rope bridges, or older buildings that have an actual structural limit don't stand a chance.

Generally a translucent green in color it turns out this color comes mostly from small pieces of grass intentionally suspended in his form, discarding them allows Cube to become significantly harder to see, almost stealthy except for the square indentation in the ground and occasional reflection of light of the still shiny surface.