What the achievement asks
Complete a Fungarian delve on tier 8 or higher without being hit by Explosive Spores. Ten points.
This is personal rather than shared. In a party of five, three people can earn it and two can fail on the same run, so nobody can carry you through it.
Activating a spore is fine. Being hit is not
This is the single most useful thing to know, and it turns the achievement from terrifying into merely careful.
Walking near a spore and setting it off does not fail the achievement. Only taking damage from the explosion does. So the moment you hear one wake up, you have not lost: you have a few seconds to walk away, and it will detonate harmlessly behind you.
Plan each pull with somewhere to run to. And ignore anything optional: gathering nodes, bonus objectives, extra packs. Slow and deliberate wins this and nothing else does.
Keep an eye on your combat log for spore damage, or run an achievement-tracking addon that announces the failure. Finding out at the boss that you lost it forty minutes ago is the worst way to spend an evening.
If you play a pet class, your pet taking a spore hit does not count. Only you.
There are only two Fungarian delves
Fungal Folly on the Isle of Dorn and Mycomancer Cavern in Hallowfall. Those are your two attempts per rotation, so if today's stories in both are awkward, waiting a day costs nothing.
The stories worth waiting for
Mycomancer Cavern, Mushroom Morsel. The boss dies at the start of the delve rather than the end, which means a failed attempt costs you a minute instead of half an hour. If you are going to fail a few times, fail here.
Mycomancer Cavern, The Great Scavenger Hunt. The first collection is in the water, away from spores entirely. The middle section is the hard part. At the end there are two islands, and when the boss casts Sporesong you simply run to the other island.
Fungal Folly, Explorer's Competition. Players report reaching every explorer without waking a single spore. For the final boss, kite him to the large rock at the south end of his platform and hug it, watching for his charge, which can knock you off the ledge.
The general boss rule
Every Fungarian boss telegraphs its spore phase before it happens. The spores it spawns explode on their own timer and do not chase you, so the answer is always the same: hear the cast, walk out, come back in. Do not try to keep hitting it through the phase.
Where it fits
One of the pieces of Glory of the War Within Delver, which rewards the Ivory Goliathus mount and is part of Worldsoul-Searching, the War Within meta.