For the records, Nagi + prince buff is enough to 3shot the green thingies. I just used a soldier + prince and used Nagi's skill just as the first green thingies got into range, then placed units i needed for nurarihyon. Healer wasn't out until the ushi-oni was about to hit my soldier and at that point nura was dead (and i even had a mage out already for the claw thingies).

To clarify - Soldier just the spot next to Nagi, prince above so he won't get hit by green things. Soldier did the 3rd hit and did not take damage from the thingies.