Uni, Bi and Tri

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Across
  1. 3. A dance
  2. 4. Has three events
  3. 5. A mythical creature
  4. 6. Together
  5. 7. 3 of something
  6. 8. Something to do with muscles
Down
  1. 1. Something with two wheels
  2. 2. Happens twice a year
  3. 4. Something with 3 sides
  4. 5. An only one