These spectres are pretty good at clearing maps, as long as you convocate them a lot a they are slow and can't keep up with player. They use cold projectile which does all the clearing, they also have short range 'spore blast' spell on 12 sec cd and a mortar spell all deal cold damage.

PoB: https://pobb.in/OVEKm6fGW7od

https://poedb.tw/us/Primal_Reborn#PrimalRebornHarvestLanternMinerT3

Get them from blue crops in Harvest sacred grove. They spawn as rare mob.

This video was recorded on standart league.