Rainbow arrow with snake decoration

Welcome! All important ingredients of this answer are from here.

documentclass[tikz,border=3mm]{standalone}
usetikzlibrary{shadings,fadings,arrows.meta,bending,decorations.pathmorphing}
pgfdeclarehorizontalshading{rainbow}{100bp}{% https://tex.stackexchange.com/a/344548/194703
  rgb(0bp)=(1,0,0);
  rgb(26bp)=(1,0,0);
  rgb(33bp)=(1,.5,0);
  rgb(40bp)=(1,1,0);
  rgb(47bp)=(0,1,0);
  rgb(54bp)=(0,1,1);
  rgb(61bp)=(0,0,1);
  rgb(68bp)=(1,0,1);
  rgb(75bp)=(.5,0,.5);
  rgb(100bp)=(.5,0,.5)}
begin{tikzfadingfrompicture}[name=my arrow]
 draw[transparent!0,ultra thick,decorate,decoration={snake,post length=2mm},
 -{Stealth}] (0,0) -- (2,0);
end{tikzfadingfrompicture}%
begin{document}
begin{tikzpicture}
 path [ postaction={shading=rainbow, path fading=my arrow, fit fading=false}] 
 (-1,-0.2) rectangle (1,0.2);
end{tikzpicture}
end{document}

BTW, for the future it would be great if you could post what you have tried.