- Not available on that edition (the reason is in the tooltip)
- Depends on the setting, your class or another addon (details in the tooltip)
What it does
Checks how many casts ago the pet spell you choose was cast, compared with the number you set, where 1 means the most recent cast. Your own casts and your pet's are counted together, and only casts within the remembered history time are kept.
Why you might use it
Check how many pet casts ago your pet used an ability, where 1 is its most recent cast. Use it to follow up right after a pet ability, such as a burst of damage just after a Succubus's Seduction lands, or to avoid repeating one too soon; casts older than Pet Spell History Memory (seconds) in the main Rotation Master options are forgotten. On Retail and Forever a cast of a spell the game hides is recorded as unknown, and that position is unavailable. See also Pet Spell Cast History Time and Spell Cast History.
Example
Seduction was cast at most 1 casts ago
Settings
What each setting in the condition editor means, from the game's own help.
The icon next to the spell name will automatically update to display the spell that is currently selected. You can drag a new spell from your spell book or action bars into this icon slot to replace your selected spell.
Use this exact spell rank - Unticked (the default), any rank of the spell matches. Ticked, only the rank you chose matches. (only on Classic Era, TBC Anniversary, Forever)
Spell - This is a specific spell used in this condition. You may drag this spell from your spell book or action bars into the input field or spell icon to set this value. This input field has prediction enabled, so you do not have to type the full spell name, just select from the prediction frame when it appears.
Operator - How to compare Pet Spell Cast History with the Count value. This comparison uses basic mathematical comparison operations.
Count - How far back in your spell history to look for a casting of Pet Spell (by count). A value of 1 means your last spell cast, 2 means two spells ago, etc. Each instance of the same spell cast is treated separately. Any spell cast more than the setting of Pet Spell History Memory (seconds) in the primary Rotation Master configuration screen ago will not be available.