Cadence have the ability to restore ponies formal and better feelings and emotions, thay may mean she have the power to restore a Unicorns fully potential magic source to cast any kind of magic…
 
And yes it was Shiny’s barrier spell that repelled the Changies, not love.
 
So Love is the perfect fuel for everything, even mass extinction of an entire race if wanted :D

Let’s forget the spell’s effects, and instead discuss the casters while they were performing their spell, if we must argue about something.
 
I theorise that pooling magical energy and cooperatively casting a spell is actually very risky business, because up until now, nopony had ever been seen attempting it.
 
Observe what happens shortly after this clip passes. They appear to reach a state where they seem to temporarily lose their physical form, becoming something sublime and held together only by the strength of the magic they were using. Imagine what could go wrong if the spell burned out of energy before it was successfully cast, or if they became too distracted to focus. In that state of having no physical body, the consequences could be fatal.
 
Then there are other variables that could become even more of a problem with the more Unicorns involved. What if one Unicorn cannot control their share from the pool of energy, and basically becomes overloaded with raw power that they are not used to? Could a pony being stressed with power higher than their natural capacity stand a chance of escaping injury or worse if they are joint-casting with others? Is it possible that a stronger Unicorn could take a larger brunt or even all of the power? It seemed like Shining Armour cast the spell by himself, and Cadence only provided the energy, which would mean that he took the full power from the pool and channelled it into his spell. However, we know that Shining Armour can cast extremely large and powerful spells, which suggests that he has a very high capacity - possibly greater than Cadence’s. But what if there were three averagely-powerful Unicorns trying to cast a spell? Would they all have to know the spell and cast it together, or could one Unicorn take all of the energy and cast it by themself, with the other two only acting as power sources?

Shinra Tensei!

Why didn’t anyone made a over 9000 joke yet ?

Christ, how many times have we gone over this?
 
It was Shining’s shield spell powered by Cadance’s love.
 
It’s like being hit with a car that was fueled by love exploding in all directions.

or at least, that’s my theory

@StuperMario
 
Think about it, blood is needed for your body, but too much blood is a very very bad thing

This some G Gundam?

Love would only make the changelings stronger. Therefore what defeated them wasn’t love…