A while back there was a whole post about making it snow in your terminal [1]. I think my favorite was [2]:
while sleep 0.1; do printf "%-$(( ( RANDOM % `tput cols` ) - 1))s\e[0;$(( 30 + ($RANDOM % 8) ))m*\n" ; done
[2] https://news.ycombinator.com/item?id=38654884