Here's a 1-day sample of the results with each tool based on MY experience:

Snorkel and Mask (10 digs)

8 Relics
2 Bones
0 Prizes
0 Traps

Oxygen Tank (15 digs)

10 Relics
4 Bones
0 Prizes
1 Trap

Diving Suit (20 digs)

10 Relics
6 Bones
2 Prizes
2 Traps

Propeller (25 digs)

13 Relics
8 Bones
2 Prizes
2 Traps

Robot (30 digs)

19 Relics
10 Bones
1 Prizes
0 Traps

Now, let's focus on the Bones gotten. We'll assume with our other digs, we got enough Relics to barter for the better tools for the various amounts of digs per day for these dates:



So:
Day 1 - 2: 4 Bones
Days 3 - 5: 12 Bones
Days 6 - 9: 24 Bones
Days 10 - 13: 32 Bones
Days 14 - 16: 30 Bones
Final total: 102 Bones

Still 60 Bones short of Devoted Indigo - time for Mines

Looking at my history with Mine usage in a single day (3 mines for 1 pass):

2 Bones
1 Prize
0 Relics
0 Traps

If I continued to have this luck with single mines...I'm looking at 30 passes to make up my missing 60 Bones (2 bones each time ; 2 x 30 = 60).

If we calculate this with my results based off a run with Double Mines (6 mines for 1 pass):

3 Bones
2 Prizes
1 Relic
0 Traps

This comes out to only needing 20 passes (3 bones each time ; 3 x 20 = 60)

Of course, again - these are just rough numbers based off single day observations. The final amount of passes does not take into account:

Mines gotten for bartering extra relics (12 Relics = 1 mine)
Multiple Digs in the same day with different tools*

*Important! Use all your digs for the day with your current tool before bartering for the next one! I used 5 out of 15 digs with the Oxygen Tank - then traded for the Diving Suit. My dig count was reset to 20, and I basically lost 10 digs. However, I used all 25 digs from the Propeller - then traded for the Robot...and was reset to 30 digs.

If don't want to read the whole thing, what it essentially boils down to is:
If the promo goes for 16 days (as it does on preprod), you will probably need ~30 passes.
I have done the math out to 20 days, which you can find below.

Ok, so I have updated my statistics for the Underwater Excavations and have some new numbers. These should be much more accurate. Just keep in mind that there is some variables in these that may affect how many passes you will need to spend to get Devoted Indigo.

One big change here is the added option to exchange relics for mines. After you have made your final equipment barter (80 relics for 30 digs per day), you will have the option of bartering 12 relics for 1 mine.

In order to get enough bones to complete Devoted Indigo, I had to do 673 digs. I did 298 regular digs and 375 digs with mines. Here are the percentages I had for each item we can find:

Regular Digs:
- Relics: 59%
- Bones: 29%
- Traps: 6%
- Prizes: 6%

Mine Digs:
- Relics: 58%
- Bones: 25%
- Traps: 0%
- Prizes: 17%

And then I did some math in an attempt to see how many passes we might need to complete it. I'll lay it out for you here.

On Preprod, the Underwater Excavation promo is going for 16 days (May 13th to May 28th). The number of digs we can do each day goes up every few days as we barter for better equipment. What we have been able to do are as follows:

Days 1 and 2 (13th and 14th): 10 digs per day
Days 3, 4, and 5 (15th, 16th and 17th): 15 digs per day
Days 6, 7, 8, and 9 (18th, 19th, 20th, and 21st): 20 digs per day
Days 10, 11, 12, and 13 (22nd, 23rd, 24th, and 25th): 25 digs
Days 14, 15, and 16 (26th, 27th, and 28th): 30 digs

We can only go up to 30 digs per day. After you have bartered for 30 digs, you are able to barter 12 relics and receive 1 mine. With all of my leftover relics, I was able to receive 16 free mines.

If the promo only goes for 16 days, as it does on Preprod, we should have approximately 405 total digs (if you use all of your digs prior to bartering for new equipment. i.e., use up all 15 digs before bartering for 20 digs. Your counter will be reset to 20 regardless of how many digs you have left. If you have 0 digs left, you will have the best advantage as it will be reset to 20). If the above percentages hold true, we should find approximately 117 bones. Which means that we would still need 45 bones. Based on the above percentages, we would need approximately 180 additional digs (with mines). If you only buy mines when they have the double mines special going on, that would equal 30 passes. Keep in mind that you will be able to barter your extra relics for mines, so this could save you some passes

Its possible that the promo will be longer once it goes live (let's hope so!), so I did some calculations out to 20 days. For days 17, 18, 19, and 20 we would be getting 30 digs per day. In this case, we should find approximately 152 bones through daily digs. We would need 10 more, or approximately 40 digs. This would equal about 7 passes if you only buy during the double mines special. Again, you may be able to save passes by bartering relics for mines.

Please keep in mind that there are quite a few variables in this, so these calculations may not be entirely accurate. According to my calculations above, it should only take about 595 digs (over 16 days) to get enough bones for Devoted Indigo. But you will notice that it took me 673 digs. This is partly because I used a lot more mines, and you actually find less bones using mines than you do during regular digs. But I'm sure that there are other factors that played a role in this, so please keep that in mind. Also, if you notice any errors in my math, please say so! I would like this to be as accurate as it can be.

How you can get, the divine in the surking sands? with the HOP? or passes?

You will be able to purchase mines for passes. One mine = one dig. Packs of 3 mines will always be available for 1 pass, but they will have a double mines promo where you can get 6 mines for 1 pass.

The last one is known
I believe it's called Brave Purple