Power effect info for Tempest's [Wrathful Blade] attack:
144.57 lethal damage on target
2 Ticks of 18.07 lethal damage over 1.10s on target after 0.50s delay
85.75 heal on self after 1.50s delay (Ignores buffs and enhancements, unresistable)
-50.00%% resistance to healing for 15.00s on target (Ignores buffs and enhancements)
-15.00%% regeneration rate for 15.00s on target (Ignores buffs and enhancements)
-15.00%% recovery rate for 15.00s on target (Ignores buffs and enhancements)
Edited for clarification:
I assume that the effect is meant to buff 'self', not the target of the attack, but so it does.
The pet in question is an LT rank pet with 857 HP fighting in melee range and, like all Core Lore melee LTs, goes down in seconds without support, when confronted with hard targets on high diff.
So, buffing the effectiveness of heals on itself would make sense and would make KoV Lore a great alternative for all kind of Support toons. Debuffing an enemy's ability to heal would make sense too, when considering the design of other Core Lore LTs and the KoV Lore boss pet. Buffing its targetted enemy makes no sense at all and I think someone simply picked the wrong effect or the wrong beneficiary.
/Edit
Below: 2 pics where Romulus Nictus' selfheal can be seen while being under the power's effect (4.242 hitpoints healed) and while not (2.827 hitpoints healed).