Step 1
Scyther used Swords Dance!
Scyther's attack rose greatly!
Diancie used Diamond Storm! -3EN
Hit (228, d240): 216 (Yes)
Crit (10, d240): 236 (No)
Effect (120, d240): 215 (No)
(10+3+(7-9))*2 = 22 DMG
Step 2
Scyther used Roost!
Scyther landed to catch it's breath! +10EP
Diancie used Diamond Storm! -3EN
Hit (228, d240): 2 (Yes)
Crit (10, d240): 168 (No)
Effect (120, d240): 190 (No)
(10+3+(7-9))*1.5 = 17 DMG
Round Summary

HP: -0

EN: -3-3 = -6

EP: -22+10-17 = -29