[Tyhm]

Clever people find ways around.

setstring oldx0,#v(playerx);
for(this.i=1;this.i<5;this.i++) setstring oldx#v(this.i),#v(strtofloat(#s(oldx#v(this.i-1))));
will create an "array" of 5 strings, oldx0, oldx1, oldx2 oldx3, oldx4

multidimentional strings are noticably easier than multidimentional variables:
setstring oldx0-0,#v(playerx),#v(playery);
for(this.i=1;this.i<5;this.i++){
for(this.n=1;this.n<5;this.n++){
setstring oldx#v(this.i) #v(this.n),#v(strtofloat(#s(oldx#v(this.i-1)-#v(this.n-1)
)));
}
}
will create an "array" of 25 strings, oldx0-0, oldx0-1, oldx0-2 oldx0-3, oldx0-4...
I botched the creation a little, you'd need to set the column oldx0-n and the row oldxn-0 for that snippet to work, but you get the idea.

this.strings are kinda tricky, but if you only need one, and the NPC doesn't have any showimgs(this version NPCs have to show to show images, and drawunderplayer NPCs make drawunderplayer images, it's weird), and it doesn't have to be visible, just use setcharprop #n,string; !