He does not do much himself (harmful effect of Leech is just to recover some health for himself.) The main threat of him is that he can summon other Undead allies after charging for three turns. As an undead himself, he will also revive three turns after knockout unless all other allies have already been knocked out.
Clearing this stage will also unlock the Star Reef harvest spot.
Undead (Revive 2-3 turns after being knocked out.)
These spooky pigs are Undead. They revive after being knocked out as long as there is a pig standing!
Hint: Try to knock out as many undead pigs as possible at the same time.
The player has to engage 1 Necromancer, 1 Zombie and 2 Ship's Kobold. Each enemy's stats are shown below.
Choose Matilda in Druid, Bomb in Cannoneer and The Blues in Rogues. Heal with Matilda if the birds' health are not full and if they're full, attack with her. Then attack with the others (All attacks focus on the Necromancer first, then the Zombie and the last one, Ship's Kobold). Repeat this over until you win or either lose.
Necromancer can use Life Leech to heal himself, so he must be defeated quickly! The Ship's Kobold can stun you, so watch out for that too.