The best replacement for unicorn is pegasus.

The best alternatives to unicorn are rated as following:
★★★★★  pegasus
★★★★  narwhal
★★★  passenger
★★★  dragon
★★  unicorn
★★  dolphin
★  pulsar
★  thin
★  werewolf
★  nginx
★  ninja
★  sinanju
★  cbz
★  unicorn_rails
★  pulsar 150
★  winmau
★  apache
★  bajaj pulsar
★  earth pony
  an unicorn
  unicorn dazzler
  puma heroku
  robot
  stunner
  gunicorn
  karizma
  puma
  dolph
  harrows
  bunyip
  fz16
  evil unicorn
  trigger
  passenger 3
  dazzler
  zombie
  flying spaghetti monster
  pony

Your alternative for unicorn is not listed? Suggest!
Speaking about unicorn, one probably shouldn't forget about rainbow.

Other search terms related to unicorn and their ratings are:
★★★★★ rainbow
★★★ nginx
★★★ rainbow coloring page
★ fairy
★ sinatra
You have in mind a companion for unicorn and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of unicorn in all years. Click on graph for more.
unicorn
pegasus
narwhal