Physical mutations cause the mutant to look differently than he or she had before. Usually these are permanent mutation, meaning that the mutant is stuck looking this way once the power has manifested itself. As these mutants are obviously different from non-mutated humans, they may find themselves subject to ostracism or anti-mutant? violence.
Physical mutations take many forms and may: change hair, skin, or eye colour; cause the mutant to grow fur or a tail; cause physical features to change shape.
Marrow is an example of a mutant with a physical mutation (both on XMR and in canon). Large bone outcroppings emerge from her skin in various locations (generally around joints as 'shields' and as spikes at the elbows and back) and her hair is naturally purple in colour.