The tail droprate is insane.

[Shucks]

I got a pink tail and a rainbow pudding.

Tried to get a black tail for achievement 3 hours and 200+ sirens later and nothing :(

[Moogy]

i know man, its beyond crazy.

Cant believe there isnt a mod yet that increases drop rate by even a teensy bit.

[Shucks]

Ill probs keep trying but damn i feel like 2% would be great.

[Ryu Fireheart]

I got enough tails to equip all party members (still only having 1 onion armor because i got bored and i aready had 5 adamant armor). And it took many hours to get them all. To make it easier i had the game in windowed mode so i could watch videos and do some other things while still being able play.
I usually reset the game if i use too many sirens, its a waste of money. Also i try to change the order of the party members once i feel like im in a bad RNG for long time.
This was the most boring thing i did in a FF game along with lv 99 in all jobs in FFIII...

[Apoc]

I just spent about 20h getting one of each tail. It's totally random but in case anyone want to know what they are getting into.

All that with Treasure Hunter, I would not try it without it. For some reason I was very lucky then it got worse and really bad for the Black Tail. They all have the same drop rate so the tail itself does not matter but the monster itself can make it a drag even if it's a similar number of sirens.

Pink Tail + Rainbow Pudding = 20-30 Sirens
Blue Tail = 20-30 Sirens
Green Tail = 100-150 Sirens (Hard to count since they also drop Sirens.)
Yellow Tail = 100-150 Sirens (Hard to count since they also drop Sirens.)
Black Tail = 500 Sirens (Because of Self-Destruct and Counter combined, that took about 7 hours...)
Red Tail = 180 Sirens (Counter and high hp made it slow and painful but no Self-Destruct at least.)

[Valtain]

Siren in flan princess room, reset and reload if I dont get a tail.
4 days and counting with no tails.

Found save editors online but they seem to be for the phone version, not using cheat engine as it makes my anti virus go crazy with warning about MAL and pua stuff.

[BlackKnightJack]

I must have been really lucky because, apart from the Pink Tail, I got all the other tails in less than 99 sirens.

[Ryan Paul Fialcowitz]

I found the game became much more enjoyable when alternative methods were used to obtain such items.