The Resonating Cleave node in Void Cleave triggers Abyssal Echoes on use and uses its mana cost, but it also uses Abyssal Echoes mana cost when Void Cleave is echoed, while other echoes do not use mana.
I’m not sure if this is technically a bug, since it’s the Void Cleave being echoed not Abyssal Echoes itself, but it still contradicts the general behaviour of echoed skills not consuming mana at all.
echo echo echo lol