[DustyPorViva]

And for those who want just the code:

PHP Code:

//NPC made by Dusty
if (created) {
  this.speed=.4; // Customize the NPCs speed

  // MODE 0 : idle
  // MODE 1 : aimless walking
  // MODE 2 : chasing via player-npc
  // MODE 3 : chasing via tracking players movements
  this.mode=0;
  setstring this.animations,idle,walkslow,walk,walk;
  showcharacter;

  timeout=0.05;
}

if (timeout) {
  if (this.mode in {0,1}) {
    this.delta={(playerx+2)-(x+1.5),(playery+2)-(y+2),((this.delta[0]^2)+(this.delta[1]^2))^.5};

    if (this.mode==0) {
      if (random(0,100)<3) {
        dir=int(random(0,4));
        this.mode=1;
      }
    }
    if (this.mode=1) {
      if (onwall(x+1.5+vecx(dir)*2,y+2+vecy(dir)*2)) dir=(dir+2)%4;
      else {
        x+=vecx(dir)*(this.speed/2);
        y+=vecy(dir)*(this.speed/2);
      }
      if (random(0,100)<6) dir=int(random(0,4));
      if (random(0,100)<2) this.mode=0;
    }
    this.checkdir=getdir(this.delta[0],this.delta[1]);
    if (this.checkdir==dir && this.delta[2]<15) checkbetween();
  } else {
    calculatetracking();
    dir=getdir(this.delta[0],this.delta[1]);
  }

  if (this.mode==2) {
    this.delta={(playerx+2)-(x+1.5),(playery+2)-(y+2),((this.delta[0]^2)+(this.delta[1]^2))^.5};
    if (this.delta[2]>3) {
      checkbetween();
      this.addx=(this.delta[0]/this.delta[2])*this.speed;
      this.addy=(this.delta[1]/this.delta[2])*this.speed;
      x+=this.addx;
      y+=this.addy;
    }
  }
  if (this.mode==3) {
    this.delta={(this.trail_x[this.step]+2)-(x+1.5),(this.trail_y[this.step]+2)-(y+2),((this.delta[0]^2)+(this.delta[1]^2))^.5};
    this.addx=(this.delta[0]/this.delta[2])*this.speed;
    this.addy=(this.delta[1]/this.delta[2])*this.speed;
    x+=this.addx;
    y+=this.addy;
    if (this.delta[2]=<.5) {
      this.step++;
      checkbetween();
    }
  }
  setcharani #I(this.animations,this.mode),;

  timeout=0.05;
}

function calculatetracking() {
  this.timer=(this.timer+.5)%2;
  if (this.timer==1) {
    if (playerx!=this.trail_x[arraylen(this.trail_x)-1]||playery!=this.trail_y[arraylen(this.trail_y)-1]) {
      setarray this.trail_x,arraylen(this.trail_x)+1;
      setarray this.trail_y,arraylen(this.trail_y)+1;
      this.trail_x[arraylen(this.trail_x)-1]=playerx;
      this.trail_y[arraylen(this.trail_y)-1]=playery;
    }
  }
}

function trackplayer() {
  this.trackdistance=100;
  for (i=0;i<arraylen(this.trail_x);i++) {
    this.delta={(this.trail_x[i]+2)-(x+1.5),(this.trail_y[i]+2)-(y+2),((this.delta[0]^2)+(this.delta[1]^2))^.5};
    if (this.delta[2]<this.trackdistance) {
      for (w=0;w<int(this.delta[2]);w++) {
        this.check={x+1.5+(this.delta[0]/this.delta[2])*w,y+2+(this.delta[1]/this.delta[2])*w};
        if (!onwall(this.check[0],this.check[1])) {
          this.trackdistance=this.delta[2];
          this.step=i+1;
        }
      }
    }
  }
  this.mode=3;
}

function checkbetween() {
  this.checkdelta={(playerx+2)-(x+1.5),(playery+2)-(y+2),((this.checkdelta[0]^2)+(this.checkdelta[1]^2))^.5};
  this.checkingwall=0;
  for (i=0;i<int(this.checkdelta[2]);i++) {
    this.check={x+1.5+(this.checkdelta[0]/this.checkdelta[2])*i,y+2+(this.checkdelta[1]/this.checkdelta[2])*i};
    if (testplayer(this.check[0],this.check[1])<0) this.checkingwall+=onwall(this.check[0],this.check[1]);
  }
  if (this.checkingwall>0) {
    if (this.mode==2) trackplayer();
  } else {
    if (this.mode==3) {
      this.mode=2;
      setarray this.trail_x,0;
      setarray this.trail_y,0;
    }
    if (this.mode<2) this.mode=2;
  }
} 


Again, sorry it's not GS2/serverside compatible.