@ShimmeringStallion  
Hmm hmm, I’ll go with that.

@Ping_chan  
Pinkie feeds off the existence of all things in Equestria.
 
Laughter’s just, like, a spice.

That pic makes me think of Excel Saga. Eeeuw that means Sonata has Tacobulosis!

@ShimmeringStallion  
Yes but,  
Changelings feeds off of love.  
Sirens feeds off of anger.  
Pinkie Pie feeds off of laughter.

@Ping_chan  
We already all know Pinkie’s a strange magical creature. It’s canon in the show, comic, graphic novel, video game, audio tapes, and colouring book.

You know what guys? I was thinking about how changelings feed from love, sirens feed from anger, and while thinking about how if that kind of system was flawed or not, I just had another idea, one that probably someone else probably thought of elsewhere out there…  
But, what if, Pinkie Pie is really another kind of strange magical creature, similar to changelings and sirens, who feeds off of laughter?  
Even if it isn’t for sustenance reasons, but the more ponies who find joy around her, the more powerful she becomes, hence her 4th wall abilities!

@BasedPharaoh  
Well like you literally just said, it depends on the number of creatures, but if there’s creatures that don’t get effected by their mind-control or that can’t have power absorbed, their power simply cannot increase as a result. There IS a ‘limit’ based around who’s available to absorb their power from.
 
@Scrounge  
What if it simply comes to be that none is around? Heck; if they find angry individuals, Discord could always mess with them and make them unnaturally happy…

@Ping_chan  
Ah. Now I understand.
 
But my guess is that if they encounter people who don’t get angry, they probably just go find a more receptive audience.

@Scrounge  
I’m just playing on the idea that the Sirens need anger to feed, so if they encounter people who do not become angry they starve to death.

@Ping_chan  
I didn’t think it through that deeply.

@Scrounge  
Which probably means that something like this would be the death of them?

@ShimmeringStallion  

 
In this case, resources seems more likely. The sirens have to absorb more hostility to get more powerful for the successive phases of the plan, which suggests that either they use it up as fuel, or they simply need certain amounts of it present to use their abilities at certain levels.

@ShimmeringStallion  
Nothing says the magic of friendship didn’t exist in Starswirl’s time, just that he himself didn’t have it. Same practical upshoot, but vastly different implications,
 
I suspect, thought I doubt it will ever be addressed, that Sunset’s immunity from the sirens, and her ability to join the others in the final battle, are because of the lingering influence of the Elements of Harmony after her defeat in the first movie (and, obviously, the way she’d turned herself around since them.)

@ShimmeringStallion  
Well despite you thinking harmony =/= friendship, Celestia still tells Twilight that Starswirl never understood the magic of friendship, which means it was around when he was around, and he banished the dazzlings, soooooooo… it kind of did exist.
 
There are no resources to their magical power. They sing. It happens. Bam. And also, you can’t evolve against something that isn’t around. I’m not going to go on paragraphs explaining how evolution works. And on top of it, the power gets stronger as the number of creatures under their spell increases.

@BasedPharaoh  
Actually, they were different at that point. The elements reacted to them back then, but no longer worked that way when the Mane Six discovered them. Heck: Celestia used them SOLO, so that doesn’t even apply. Harmony =/= Friendship (Or at least, it didn’t, for a time).
 
How is it possibly the case to assume there’s no end to any form of power? It’s limited by resources, or by the power itself. It’s also an assumption that ponies could’ve changed in all the years that they existed as a form of ‘evolution’. There’s a lot of assumptions until proven with facts rather than theoretical evidence…
 
Otherwise we could just say “Mirror pond” and assume it gets exploited again by Sirens or Tirek.

@ShimmeringStallion  
uh huh….  
the magic of friendship always existed. Do you not remember Celestia and Luna having to use the elements of harmony against discord, or the fact that Celestia had explained to Twilight that Starswirl never UNDERSTOOD friendship?
 
Also they never explain the limit of their power, so it’s safer to assume that there isn’t one. And if natural equestrians were immune to their mind control spell, then they would’ve never had been a threat in the first place and Starswirl would have never banished them because everyone in Equestria would’ve been immune, but they weren’t.

@BasedPharaoh  
Well they gave Trixie the incentive to do so on-screen, but could’ve told her about the trap off-screen, in case someone found out and would need to take the fall…
 
Also, in Starswirl’s time, the magic of friendship didn’t exist, as opposed to now, which obliterated the sirens’ powers. Previously, they could only trap them, so they had limitations.
 
Lastly, their mind-control powers were towards certain creatures, and immune to other ones. Sunset shouldn’t have been immune, yet she was; maybe it doesn’t work on natural Equestrians?

@ShimmeringStallion  
whoa ok now youre bringing up stuff we are not even talking about.
 
Plus they seemed like a force to be reckoned with on equestria so I don’t see why you’d think they wouldn’t be able contend, especially considering they have the power of mind control.  
Not to mention their foresight had to have been 10/10 considering they somehow knew Trixie would trap the main cast under the stage and bout beat them in combat, outnumbered

@BasedPharaoh  
Well how would she know others wouldn’t be immune to the power, too? Really, the tree of harmony and “magic in the box” would be more than enough to stop them, especially if they still have five of the elements, and a box filled with deux ex machina…
 
The problem is more along the lines of “what else would they be capable of doing after obtaining power”, since Starswirl cut them off early. Even with ‘logical steps’, they seemed pretty set on just returning to Equestria, not that they’d have much of an ability to do much else once they were there, since they’d be met face-to-face with new creatures.
 
Though I guess you explained why they’d need power, even if their purpose is pretty basic and prone to a lack of foresight (Discord, element bearers, alicorns, changelings).

@ShimmeringStallion  
what are you talking about? This information is all gathered from canon resources, where Twilight takes out a book and describes the Sirens and what they did and how they did it.
 
When I say “started” I meant the start of their huge scheme to get, as adagio put it, “to get everyone on this pathetic little world to adore us”. At that time she’d only mind controlled a high school, if they defeated the mane 6 and SS they wouldve moved on to mind control the whole world.

@BasedPharaoh  
How can anyone determine that such is how they would’ve ‘started’? Technically, the only one who worked against them was Starswirl the Bearded, and if that’s the only experience he had, he wouldn’t know what else they were capable of.

@ShimmeringStallion  
i just told you. they need it to become stronger so they can become more powerful, which allows them to spread their magic further. The siren-form wouldve just been the beginning had they not been stopped.

@BasedPharaoh  
But why do they NEED the power? Just to become siren-forms? Yet the crystals still exist when they’re in those forms (as do their human forms)…

@BasedPharaoh  

 
Did I at any point say it would be a healthy relationship? :P
 
(Okay, the real reason I think the Sirens stick together is they’re not strong enough separately, but dysfunctional longing is an amusing alternative.)

@Scrounge  

 
you have to get along with someone to be in a healthy relationship with them
 
@ShimmeringStallion  

 
We do know why. The more they absorb, the more powerful they become. Twilight explained this in the pony part bout 20 minutes in.