The Staff?
The Staff? Start: Go to the Mysterious Cenote and pick up a staff from the chest after doing The Staff Quest.
Warning: If you haven't completed the Black Willows (delve completion also counts as a completion) at least once, this quest will silently fail to start.
First, go to Southern Village south of Sierhaven and pick up the Whirlpool coin from the fountain. Then, go behind the Lighthouse and there is an underwater grate in the water with stone blocks and iron trapdoors at -847, 78, 458. Throw the Whirlpool coin into the grate:
The torrent awakens... The Shrine has changed...
Head to Water Shrine. The Water Shrine will now be amplified and a pressure plate is on the inside to step on.
A strange new power flows into your Staff!
For the Earth Shrine, you have to go to Molten Chasm and break the 3 black concrete powder blocks sandwiched between two magma blocks scattered around the POI. Once that is finished, you will get confirmation text that this worked:
With the supporting structures broken, lava seeps into the earth, moving southwest...
Head to Earth Shrine which is now amplified. Find the pressure plate and you will have completed the Earth Shrine.
A dangerous power rumbles into your Staff!
For Fire Shrine, go to Water Cavern and go to the very bottom of it. There you should see ice on the surface of the water and a dark prismarine block with a button at [89, 31, 8], press the button to get the Ice Crystal and go to Fire Shrine. At the back of the shrine (-241, 109, 143), there is a dropper surrounded by magma blocks. Put the ice in the dropper and press the button. (NOTE: make sure to back away from the shrine as fast you can after pressing the button so there is little chance the amping is halted by your character being "in" the shrine. You'll know if it's amplified or not when the magma turns into ice.)
An icy wind blows and the fire shrine itself shudders!
Go in the shrine and stand on the pressure plate.
A dangerous flame roars into your Staff!
Tip: For Amped Air Shrine, there are invisible creepers with potions with Instant Harming 10, do NOT get hit by them.
For the Air Shrine, you must have a Narsen's Will. To start the amplification, go to Sierhaven and head East. Follow the path until you get to the 2nd house on your right; it has a glass plus sign above the door. Go inside and talk to the NPC Amelia the Pilot.
[Amelia the Pilot] Yo. I recently moved here from on top of a big tree. I had to leave my hot air balloon behind, but things were getting a bit too close for comfort, and I've never been a big fan of heights. Wait, hey, is that a Narsen's Will?
[Yes, I've got a Narsen's Will right here]
[Amelia the Pilot] That's awesome! If you ever see a balloon called the Harbinger of the Tempest, you should give them this. They'd really dig it if you know what I mean.
You will get an Eye of the Storm. Go to Hawk Fortress and find the Yellow and Light Blue hot air balloon named "Harbinger of the Tempest." Put the item in the dispenser, you will get a confirmation text:
A strong wind is blowing from the northeast...
The Air Shrine will be immediately amplified next to you. Find the pressure plate inside.
A raging tempest screams into your Staff, completing it with a bright flash!
You know where you must take it.
You should now have a completed staff, now go to the Cave of Secrets and step through the portal.