Insulator-metal-superconductor transition in the medium-entropy van der Waals compound <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>M</mml:mi><mml:mi mathvariant="normal">P</mml:mi><mml:msub><mml:mi>Se</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow><mml:mo> </mml:mo><mml:mrow><mml:mo>(</mml:mo><mml:mi>M</mml:mi><mml:mo>=</mml:mo><mml:mi>Fe</mml:mi><mml:mo>,</mml:mo><mml:mi>Mn</mml:mi><mml:mo>,</mml:mo><mml:mi>Cd</mml:mi><mml:mo>,</mml:mo><mml:mspace width="0.28em…

$M\mathrm{P}{X}_{3}$ ($M=\mathrm{metals}$; $X=\mathrm{S}\phantom{\rule{0.28em}{0ex}}\mathrm{or}\phantom{\rule{0.28em}{0ex}}\mathrm{Se}$) represents a large family of van der Waals (vdW) materials featuring P-P dimers $\ensuremath{\sim}2.3\phantom{\rule{0.16em}{0ex}}\AA{}$ separation. A dramatic alteration its electrical transport properties, such as metal-insulator transition, has not been realized by intentional chemical doping and ionic intercalation. Here, we employ an entropy-enhancement strategy to successfully obtain series medium-entropy $M\mathrm{P}{\mathrm{Se}}_{3}$ $(M=\mathrm{Fe},\mathrm{Mn},\mathrm{Cd},\phantom{\rule{0.28em}{0ex}}\mathrm{and}\phantom{\rule{0.28em}{0ex}}\mathrm{In})$, in which the magnetic properties change simultaneously. Lone-pair electrons P emerge due dissociation evidenced 35% elongation interatomic distance. The band gap widens from 0.1 0.7 eV this dissociation. Under external physical pressure up $\ensuremath{\sim}50$ GPa, giant collapse 15% $c$ axis happens, is contrast in-plane shrinkage their counterparts $\mathrm{Fe}/\mathrm{MnP}{\mathrm{Se}}_{3}$. It leads recombination ${\mathrm{P}}^{3\ensuremath{-}}$ with lone-pair into dimer smallest bulk modulus 28 GPa $M\mathrm{P}{X}_{3}$. transitions spin-glass insulator metal, superconductor, rarely observed Our findings highlight indicator probe diverse electronic structure effectiveness entropy enhancement science.