Will {Executioner's Swing} kil {Thassa, God of the Sea}?
Yes. Lethal damage and "destroy effects will not kill it, but it still dies when it's toughness reaches 0.
Sometimes they are much better being left as enchantments.
If thassa is a creature, {Turn // Burn} it!!! Problem solved.
Is a {isocrone szepter} still legal in standart, would make a veritable "godkiller" :)