Sound like the alternative conversation bureau.
Presume #. The Energy for pony magics are some kind of radioactive to human science. Equestrian Especially ponykind are emitting Energy for magic from their body.
Hypothesis #. That Radiation energy for pony magics are equally harmful as any radioactive waste. Especially Alicorns emitting energy is nearly equally as nuclear reactor.

As results Near environment of Equestrian's landing site or portal place are suffer and Either slowly or immediately dying from immense radiation until devastated everything but native equestrian are remaining.

As like any other Pony on earth and ACB prologue , Equestrian's protagonists are intended to find humanity and hope to bring peace and harmony and love between their races also especially no Intend to go ACB genocide.

Walking harmful radioactive magic catoon ponies are coming to Earth and what shall people of Earth they do?

I thought humanity's first of first Alien Contect is will not go to directly Peace and harmony. maybe go to conflict and problems or in worst case is go to war. Or in peace and harmony and in return are stagnation and depressing.

I am apologizing for any error of grammar and spelling or sentence, i am some east asian so please appreciate poor writing.

4982293

Nuke the ponies. Kill them all!

OK... They should close the portal and go back to where they came from. Or place a magic barrier, unmoving around Equestria to stop them form killing all humanity.

my story, "A New Life, or an Old Strife?" has a... similar science behind it. that, for example, as someone changes from person to pony they release magical energy, which in turn changes the environment (and creatures) around them. Which in turn, if more people come along, will ponify them. wash, rinse, repeat.