Is the Higgs boson only a particle of pure mass? It has no charge, no spin, no color, no flavor, etc. Does it have any other non-zero characteristic besides just mass?
I'm not sure what it would mean to be a "particle of pure mass", but in any case the answer is no.
The Higgs boson is a particle, not too dissimilar from other particles. It's thought to have spin 0, space parity +, charge parity +, and zero values for the various possible types of charge. The charges must be zero because they change sign under charge conjugation, and the Higgs boson is its own antiparticle.