When “Airknight Parshath” equipped with “Cestus of Dagla” inflicts damage to your opponent’s Life Points, the simultaneous effects go on a chain, so the controller decides which effect is resolved first.
If you have multiple copies of “Cestus of Dagla” equipped to your monster, the effects accumulate.
When your opponent takes control of your Fairy-Type monster equipped with your “Cestus of Dagla”, and your opponent uses the monster to damage your Life Points, neither player increases their Life Points. This is because the controller of “Cestus of Dagla” is still you, and “Cestus of Dagla”’s effect only activates when the equipped monster inflicts damage to your opponent’s Life Points. Likewise, if you equip “Cestus of Dagla” to your opponent’s Fairy-Type monster, neither player will gain any Life Points from “Cestus of Dagla”.
Netrep Rulings:
If the monster equipped with “Cestus of Dagla” is not under the control of the controller of “Cestus of Dagla,” the Life Point gaining effect of “Cestus of Dagla” does not apply.
“Cestus of Dagla” will trigger its Life Point gaining effect if the monster equipped with “Cestus of Dagla” attacks Life Points directly.
If more than one “Cestus of Dagla” is equipped to the same monster, each “Cestus of Dagla” will trigger the Life Point gain.
Netrep Q&As:
Q: If a monster equipped with “Cestus of Dagla” attacks the opponent directly, will the controller of the monster gain Life Points?
A: If you control both the equipped Fairy-Type monster AND the “Cestus of Dagla,” then you will gain Life Points equal to whatever amount of Battle Damage you have done to the opponent’s Life Points from that equipped monster’s attack. So if I have “Zolga” equipped with “Cestus of Dagla” and it attacks my opponent directly, I would gain 2200 Life Points by the effect of “Cestus of Dagla.” Curtis Schultz, 01/29/2004