Mysterious squash thing appears to be tiny (stealth) pumpkin.
Known zucchini made one nice little zuke, two that quickly became misshapen and strange, developed spots on its leaves, and now appears to be marching toward death. Fine, be that way.
Our first watermelon is coming along nicely, here pictured with with dinosaur for scale*. This is the biggest of the plant’s babies, even though it has munched approximately half the garden in its pursuit of garden domination.