RNG stands for Random Number Generator, meaning everyone will have different results.

it's random, but is not strictly required to use them, in the sense, they just make it less expensive.

the idea is to roll until you get some +1 or some yellows, then complete what you miss with frags.

doing this takes usually about 10-30 potions.

That Y skill can't be achieved with frags :/ and I want the chakra one too...

Once you've skill broken the appropriate skill with frags, you're able to swap it over to Y in the skill trial tab

nice, and I just wasted 80, then it disappeared after I refreshed again.

feel so dumb, lowkey wanna quit now. lost 500 coupons

I used 10 vials on Ningendo and finished his BT/Trial with 180 fragments I had stored, meanwhile on Gakido I used 60+ vials and only things I've gotten are Mystery +2 and +1 chase...

No idea if I'm just unlucky or it's lower chance to get Gakido's trial/bt. I remember getting Sasuke's and Tsunade's fairly quickly as well.

Gakido was so hard for me, 70 potions at least.

Yes, as they told you, you can freely change an y trial with a breakthrough of par level and viceversa (so blue with blue, purple with purple, gold with gold).

How many advanced vial and protection needed for edo deidara?

It's RNG. There is no set number. It functions just like the Purify system. It could be a few, or it could be hundreds.