At some point when playing Stardew Valley, you may need to get ectoplasm as part of a special delivery quest for the Wizzard NPC; that said, here's where and how to get ectoplasm in Stardew Valley.
Where to get ectoplasm in Stardew Valley
To get ectoplasm in Stardew Valley, you must find and defeat ghost enemies that spawn in the mines around levels 51 to 79. If you run into any problems fighting them, the best strategy to fight them is to simply stand still and swing at them with your weapon right before they hit you.
Upon hitting them, the ghost will teleport to a new location and come at you again; when this happens, simply repeat the same step until they die.
Each ghost you kill has a slight chance of 9.5 percent to drop the ectoplasm you need. Ghosts also seem to spawn rarely, so you might have some difficulties finding them.
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Luckily, there's another version of ghosts you can try to farm; they are called carbon ghosts, and they tend to spawn on the mummy levels in Skull Cavern. Carbon ghosts also have a 9.5 chance to drop ectoplasm, and they also drop omi geodes quite often, so if you want those geodes, they are a good enemy to farm for them.
That being said, once you get ectoplasm, you will then need to give it to the wizard; you can do this by simply finding the wizard over at the wizard tower as shown above and gifting the item to him.