Lorelei's Fountain just gave me a gold troll token so don't forget to put yours out, as well as your beast master statues.
Some numbers - mainly for my own benefit, but somebody might find them useful.
I got the siren on my main account. It took a bit under 1000 energy. I'm up to 50 shell tokens from about 160 energy. The remaining 450 shell tokens should take me about 1440 energy. I get about 450 energy a day, so I should have the unicorn in about three and a half days. (Sorry - not saying this to make anyone with few energy sources feel bad, just setting out my calculations).
On my other account, I have no stored energy, I get about 200 energy a day from refills, and about 80 from wizards school and a few daily alis, so I expect it will take about five days to get the siren. That means that on my baby account, I wont be doing the trees for the shell tokens, or the horses and dead trees for normal tokens until I have the siren. I think the siren is a good prize and I don't want to jeopardize it.
The following animals also spawn Sirens: heart cow, cupid pig, mummy cow, Frankenpig
I noticed royal cows/pigs and pink pigs spawn every time. My black pigs took 8 pigs to spawn.
Anyone know what the Royal Siren renders?
Queendom Name - Hyrule
Sadly my first collection from Lorelei's Fountain didn't give me a troll token . Those eels are hard to get for those who want the armored siren like me. I have used a lot of energy chopping anemones have only gotten 4.