The main problem with perish song is that it takes 3 turns to work. There are faster ways to make your opponents faint, such as this moveset.
Absol
Ability: pressure
- strength/return
- swords dance
- shadow ball
- aerial ace/iron tail
If you want to save the TM23 iron tail, TM30 shadow ball, or TM40 aerial ace for other Pokemon, use this moveset instead.
Absol
Ability: pressure
- strength/return
- swords dance
- thunderbolt
- ice beam