One Decisive Strike
Klaus knew he couldn't afford to make a mistake. Assassins are tricky; if you don't kill them with your first strike, the chance of succeeding with the next is slim.
Their escape skills are legendary, and Klaus was well aware of that. He planned to counter those skills with his own, using precision and timing.
The [Bell of Harrows] and [Eye of Despair] were the key to his success. The bell had the power to deal both physical (Sonic) and spiritual damage. Klaus needed that combination, and with the addition of the [Eye of Malevolence], he knew he had a real shot.
"Mother-in-law, I'm making my move. Be ready to step in if things don't go as planned," Klaus muttered under his breath as the bell and eye manifested in the air.