Draw a symmetric alien head

In simple cases like this you could just use a pic and mirror it.

\documentclass[tikz,border=3.14mm]{standalone}
\definecolor{maincolorMedium}{HTML}{a757b2}%
\begin{document}
\begin{tikzpicture}[pics/lhead/.style={code={
\draw[fill=maincolorMedium,even odd rule] (0,0) -- (-3,-4) -- (-3,-1) arc(270:0:3) (-3,0) rectangle (-1,2);}}]
\draw[dashed] (-6.5,-4.5) grid (6.5,5.5);
\path[fill opacity=0.4] (0,0) pic{lhead} pic[xscale=-1]{lhead};
\end{tikzpicture}
\end{document}

As a mathematical figure, it's a poor match.

But as an alien head in the style of Cthulhu, I think it gives the OP's a run for the money.

\documentclass{article}
\usepackage{graphicx,xcolor,stackengine}
\begin{document}
\bgroup
\savestack\halfhead{\Huge\stackinset{c}{3pt}{c}{23pt}{%
  \color{red!15}\rule{7pt}{7pt}}{\scalebox{10}{,}}\kern-19pt}
\halfhead\reflectbox{\halfhead}
\egroup
\end{document}

A pstricks code:

\documentclass[border = 5pt, svgnames]{standalone}
\usepackage{pstricks}
\usepackage{auto-pst-pdf}% to compile with pdflatex --enable-write18 (MiKTeX) or pdflatex --shell-escape (TeXLive, MacTeX)

 \begin{document}

\begin{pspicture}[showgrid](-6.5, -6.5)(6.5, 3.5)
\psset{linewidth=0.6pt, linecolor=Plum, fillstyle=solid, fillcolor=white}
\pscustom[fillstyle=solid, fillcolor=Plum, opacity=0.4]{%
\psarc(-3,0){3}{0}{270}\psline(-3,-6)(0,-2)(3,-6)
\psarc(3,0){3}{-90}{180} }%
\psframe[](-3,-2)(-1,0)\psframe[](1,-2)(3,0)
\end{pspicture}

\end{document}