Krakia?

An "invasion coming to Maple World" means a force from out comes in. That would rule out anything we have or have been hinted at thus far. It actually sounds like an Omega Expansion, to me.

The 'invasion' she could be referring to could be Krakians resurfacing, and therefore, 'invading' Masteria(which is part of the 'Maple World' after all).

c

That scenerio works for an 'invasion coming to Maple World'.