In 2-D: circles, ellipses, smooth loops or in 3-D spheres, ellipsoids, smoothed blobs have none.
A cone has only one vertex.
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Then you have 6 vertices. No problem.
Two triangles.
A polygon may have many more than four sides, a triangle has only three vertices.
You cannot have such a shape because either the shapes must meet at an edge or the vertices must be joined by an edge.
The angles at the vertices. A square has vertices of 90 degrees. A rhombus has two vertices greater than 90 degrees and two vertices less than 90 degrees.