triangle
A triangle or a circle.
You cannot answer this with a normal shape. Any shape given would have less an infinite sides. The exception to this would BE the shape with infinite sides and therefore by the same token, an infinite perimeter. So, the answer would be a "Fractal"
It has less than three sides.
triangular pyramid-4 equal faces
The pentagon satisfies those criteria precisely.
Common shapes with less than 4 sides are triangles and circles ( but the circle has no straight sides).
Pentagon.
a pentagon is a polygon with 5 sides not less or more.
A polygon with 4 sides has 4 angles. All polyhedra have at least 4 vertices so I cannot think of any shape that meets the requirements.
A right angle triangle
No polygon can have less than 3 angles. It would be a triangle with 3 sides but that has 3 angles.