I found a new really useful way of mining Umbris; not sure if it’s known, but I thought I’d make a step by step guide! ^-^
I’ve tried normal strip mining and layer mining, however I’ve found the most success with this method in the least amount of time! 
(A bonus to this is if you’re like me and get to exos later than everyone else, it is allot easier to mine through previous mines of other peoples, not having to fall through floors and not be able to cover as much ground due to random floating unmined blocks everywhere you walk)
Equipment
-
3x3 hammer
(prefebly a fast one with strength brew, or damaging one with speed brew) -
Brews
(Speed or strength as said above) -
Long grapple
(the longer the better) -
Pie
(either preserving or teaching) -
Atless and altitude
(To find a good hotspot worth mining, note Umbris is only found at 100 - 250 Altitude according to the wiki, however 130 is a good sweet spot)
Step 1 : Find a high altitude place with lots of umbris using an Atless
Step 2 : Clear a flat surface to mine, it makes it easier to get in and out of the mine you make
Step 2 Visuals
Step 3 : Count 4 blocks away from any previous mine so there’s a 2 block wall between them / choose the spot where you’re going to start your new mine if at a new location
You want a 2 block wall so you don’t waist durability mining excess rocks, while at the same time covering as much ground as possible.
Step 4 : Dig down 1 to mark your spot; then build up 4 creating a pillar in the centre, and mine the bottom 3 of the pillar so there is a single floating block
Step 3 / 4 visuals
Step 5 : Grapple onto that centre block, then start mining straight down as far as your grapple lets you
Step 5 visuals
Step 6 : Pull yourself back up, reap your reward and repeat!!
Step 6 visuals
I hope this helps! <3
