Looking through the script there are two reasons why the skill might not be working, that I have thought of so far.
First it is trying to restore mp to the wrong target,
Second because the effect triggers when the target dies but the debuff is also removed when the target dies it is possible it is being removed before it triggers.
Trying to edit the script to fix this myself but unsure how to make the effects print info for me to look at in the console.
Okay it was definitely option 2. I removed the remove on death from the debuff and it restored mana to the caster as expected. Only drawback is now the corpses have the debuff showing on them, it will still be removed at the end of combat, and maybe someone knows how to make it remove when triggered.
For anyone wanting to make the skill work in file "assets\data\Effects.gd"
function e_t_devour
line 2178 change
rem_event = [variables.TR_COMBAT_F, variables.TR_DEATH],
to
rem_event = [variables.TR_COMBAT_F],
as for making the skill name and description translate in file "localization\en\main.gd
Lines 694 and 695 change
SKILLDEVOURSPIRIT = "Devour Spirit",
SKILLDEVOURSPIRITDESCRIPT = ...
to
SKILLDEVOUR = "Devour Spirit",
SKILLDEVOURDESCRIPT = ...
