Old Tonic Potions should work for Mad King Chests
Most people have already used or destroyed their old tonics for a simple reason, you can make them using mesterious tonics and the mystic forge.
Heres a alternate suggestion, spend 2g getting a char to 400 artificering using cleric weps and lots of potions, at 400 you can make the required tonics for 5/[1 crystaline dust, 1 water, 1 vicious claw, 1 vicious fang].
No more non cosmetic world event rewards. We haven’t forgotten the Ancient Karka.