The title pretty much.
The Harpooned condition, is it an effect owned by the attacker, or the defender?
The underlying issue is TLT. If it's an attacker effect you can always trigger Harpooned with the TLT (as you can choose to trigger Harpooned before TLT effect), but if it's a defender effect, which triggers first depends on initiative as per FAQ:
Q: If both players have effects that resolve at the same time
(or from the same trigger), which player resolves their
abilities first?
A: The player with initiative resolves all abilities he would like to resolve, then
the other player resolves all abilities he would like to resolve.