@Boney
Aside from the sheer meme value, is there any added practical value as far as Mathilde knows to her using her knowledge of all things WAAAGH! to create a "summon greenskins" version of the Apparition spellframe?
Well in that case I would like to point out to the thread that such a spell might very well be useful as a tool for highjacking WAAAGH!!!'s into a preferred target, the apparition will be the big scary "purple ork warboss", and Mathilde will be the warboss's chief advisor and goblin shaman disguised with a mix of Ulgu illusion magic and the Deceiver face of Ranald's coin.
With this Mathilde as her identity as the purple warboss will be able to take command over various WAAAGH!!!'s and smash them into a target of her choosing like the chaos dwarfs for instance.
And because she's still a very sneaky grey wizard, it shouldn't be too hard for her to sneak and run away to WAAAGH!!! another day whenever her current WAAAGH!!! gets destroyed.
What's more, with the way Ork WAAAGH!!! energy works, as the legend of the purple ork warboss increases among the greenskins, Mathilde's Ork shaped apparition should in theory increase in power as well just like how Commisar Yarrick in 40k became that much of more of a badass due to the Orks believing him to be as such.
Which in theory should leave Mathilde with a hilariously scary Ork Warboss apparition to attack people with.
Also there's to my knowledge nothing except AP expenditure stopping us from using both the Purple Ork Warboss idea AND the Ulgu Nazgul idea.