Use a Particle system. Set it to [Hair mode](https://docs.blender.org/manual/en/dev/physics/particles/hair/index.html) and set the Render to Object. Select the object you want to use as spikes as Dupli Object. (The specified object will be duplicated in place of each particle) [![enter image description here][1]][1] Use [Weight Paint](https://docs.blender.org/manual/en/dev/sculpt_paint/painting/weight_paint/introduction.html?highlight=weight%20paint) to define the areas where you want the particles to appear. Red where you want the most particles, blue where you want none. [![enter image description here][2]][2] Then set the [Vertex Groups](https://docs.blender.org/manual/en/dev/physics/particles/emitter/vertex_groups.html) to use the vertex group created through the weight paint. [![enter image description here][3]][3] [1]: https://i.sstatic.net/gvLgG.png [2]: https://i.sstatic.net/oPjRa.png [3]: https://i.sstatic.net/ZIeTR.png