When Sett The Boss's replacement effect is used to save a buffed unit from dying, can the opponent respond with removal (like Hidden Blade) after the cost is paid but before the unit is recalled?

Ruling: No, you cannot respond. Sett The Boss's ability is a replacement effect that does not use the chain. Once the cost is paid, the unit is immediately recalled exhausted with its buff spent, with no window for response.

Sequence:

• Buffed unit would die during cleanup
• Sett The Boss's replacement effect applies
• Owner pays the cost (exhaust Sett and pay power)
• The unit is immediately recalled exhausted with buff spent
• No opportunity to respond between paying the cost and the recall happening

Nuances:

• Despite the "when" wording on the printed card, the errata makes this a pure replacement effect, not a triggered ability
• Replacement effects do not go on the chain like triggered abilities would