@FeatherTrap  
The Terik one had them used the Tree of Harmony instead of the elements.

@TheSultanAkbar  
If the show’s history is to be believed:
 

 
Or you know, the ending of that very episode:
 

 
Nothing. Nothing wrong whatsoever.  
So it’s a good thing the writers made them fucking morons that forgot they could do that, or else the drama would have been over right quick.

@FeatherTrap  
Well, ok. Let’s just blindly stand in front of the enemy and charge a friendship attack, what could go wrong?

@redweasel  
No, they still thought they needed the elements back in the pilot episode. Twilight simply realised that destroying their physical vessels wouldn’t work because she and her friends embodied the elements and they could use that to remake them. Which is another rule the Season Nine Opening forgot, so it forgot both of the previously established main rules about how the Elements of Harmony worked.
 
 
@TheSultanAkbar  
The Tree of Harmony was not required before. They simply forgot they could use their powers for half the runtime because if they didn’t then the main conflict would have been over at the end of the first part.
 

 
@Edhelistar  
Yes, that was before the Season Four Finale, when they realised the friendship was inside them all along.

@TheSultanAkbar  
Yes, they did.
 
 
@redweasel  
And in season 1 episode 2 they needed the Elements themselves.

@FeatherTrap  
Nooo… didn’t they have the tree of harmony and the chest thing?

@FeatherTrap
 
silly feather trap, that’s not how you spell “season one, episode one”

Me just sitting here thinking:  
“Remember when Twilight and friends realised the Magic of Friendship was inside them all along and they didn’t need the elements back at the end of season four?”
 
Yeah, guess the writers forgot they could do that. :I