These balls are used in Regurgitation Pumping Station at the end of Chapter 1. They are lighter than air and will helpfully lift your ivy structure into the air, so you can see the the world around you.

They also make a brief appearance in the end-game movie, carrying an ivy structure through space.

<ball name="EvilEye" 
      shape="circle,70,0.25" 
      mass="30" 
      strands="1" 
      walkspeed="0"
      climbspeed="0"
      speedvariance="0" 
      antigrav="3" 
      dampening="0.1"
      grumpy="true"
      collideattached="true"
      invulnerable="true"
      autobounds="false" 
 
      attenuationselect="0.1, 1.0, 1.1"
      attenuationdeselect="0.1, 1.1, 1.0"
      attenuationdrop="0.1, 1.1, 1.0"
      attenuationdrag="0.1, 1.1, 1.0"
      maxattachspeed="1000" 
      hideeyes="false"
      >
 
  <marker drag="IMAGE_BALL_EVILEYE_DRAGMARKER" 
          detach="IMAGE_BALL_EVILEYE_DETACHMARKER" 
          rotspeed="2"/>
 
  <shadow image="IMAGE_BALL_GENERIC_SHADOW1"/>
 
  <particles id="sleepyZzz" states="sleeping" overball="true" />
 
  <strand type="rope" 
          image="IMAGE_BALL_EVILEYE_ARM" 
          inactiveimage="IMAGE_BALL_GENERIC_ARM_INACTIVE" 
          springconstmin="2" springconstmax="2" 
          dampfac="0.002" 
          maxlen2="300" maxlen1="300" 
          maxforce="2000" 
          minlen="120"
          walkable="false"
          thickness="20"/>
 
  <detachstrand maxlen="70" />
 
  <splat image="IMAGE_BALL_EVILEYE_SPLAT1,IMAGE_BALL_EVILEYE_SPLAT2"/>
 
  <part name="body"
        layer="0"
        rotate="false"
        x="0" y="0"
        image="IMAGE_BALL_EVILEYE_BODY"
        stretch="24,1.1,0.9"
        scale="0.35"
 
        eye="true"
        pupil="IMAGE_BALL_EVILEYE_PUPIL"
        pupilinset="116"
        />
 
  <!--
  <part name="pupil"
       layer="1"
       rotate="false"
       x="0" y="0"
       image="IMAGE_BALL_EVILEYE_PUPIL"
       scale="0.35"
        />
  -->
 
  <part name="shine"
        layer="2"
        rotate="false"
        x="0" y="0"
        image="IMAGE_BALL_EVILEYE_SHINE"
        stretch="24,1.1,0.9"
        scale="0.35"
        />
 
  <!-- attached animations -->
  <sinvariance freq="0.3" amp="0.02" shift="0.8">
    <sinanim part="body,shine"             state="attached" type="scale"     axis="x" freq="1.0" amp="0.2" shift="0"   />
    <sinanim part="body,shine"             state="attached" type="scale"     axis="y" freq="1.0" amp="0.2" shift="0.1" />
  </sinvariance>
 
  <!-- walking animations -->
  <sinvariance freq="1.2" amp="0.1" shift="0.0">
    <sinanim part="body,shine"             state="walking" type="scale"     axis="x" freq=".20" amp="0.03" shift="0"   />
    <sinanim part="body,shine"             state="walking" type="scale"     axis="y" freq=".20" amp="0.03" shift="0.5" />
    <sinanim part="body,shine"             state="walking" type="translate" axis="y" freq=".20" amp="2"   shift="0"   />
  </sinvariance>
 
  <!-- falling animations -->
  <sinvariance freq="1.2" amp="0.1" shift="0.0">
    <sinanim part="body,shine"             state="falling" type="scale"     axis="x" freq=".20" amp="0.03" shift="0"   />
    <sinanim part="body,shine"             state="falling" type="scale"     axis="y" freq=".20" amp="0.03" shift="0.5" />
    <sinanim part="body,shine"             state="falling" type="translate" axis="y" freq=".20" amp="2"   shift="0"   />
  </sinvariance>
 
  <!-- dragging animations -->
  <sinvariance freq="1.2" amp="0.1" shift="0.0">
    <sinanim part="body,shine"             state="dragging" type="scale"     axis="x" freq=".20" amp="0.03" shift="0"   />
    <sinanim part="body,shine"             state="dragging" type="scale"     axis="y" freq=".20" amp="0.03" shift="0.5" />
    <sinanim part="body,shine"             state="dragging" type="translate" axis="y" freq=".20" amp="2"   shift="0"   />
  </sinvariance>
 
 
 
  <!-- Sound FX -->
  <sound event="marker"       id="SOUND_BALL_GENERIC_ROLLOVER1,SOUND_BALL_GENERIC_ROLLOVER2,SOUND_BALL_GENERIC_ROLLOVER3,SOUND_BALL_GENERIC_ROLLOVER4,SOUND_BALL_GENERIC_ROLLOVER5,SOUND_BALL_GENERIC_ROLLOVER6,SOUND_BALL_GENERIC_ROLLOVER7,SOUND_BALL_GENERIC_ROLLOVER8"/>
  <sound event="pickup"       id="SOUND_BALL_GENERIC_PICKUP1,SOUND_BALL_GENERIC_PICKUP2,SOUND_BALL_GENERIC_PICKUP3,SOUND_BALL_GENERIC_PICKUP4,SOUND_BALL_GENERIC_PICKUP5,SOUND_BALL_GENERIC_PICKUP6,SOUND_BALL_GENERIC_PICKUP7,SOUND_BALL_GENERIC_PICKUP8,SOUND_BALL_GENERIC_PICKUP9,SOUND_BALL_GENERIC_PICKUP10"/>
 
  <sound event="drop"         id="SOUND_BALL_GENERIC_PICKUP1,SOUND_BALL_GENERIC_PICKUP2,SOUND_BALL_GENERIC_PICKUP3,SOUND_BALL_GENERIC_PICKUP4,SOUND_BALL_GENERIC_PICKUP5,SOUND_BALL_GENERIC_PICKUP6,SOUND_BALL_GENERIC_PICKUP7,SOUND_BALL_GENERIC_PICKUP8,SOUND_BALL_GENERIC_PICKUP9,SOUND_BALL_GENERIC_PICKUP10"/>
  <sound event="throw"        id="SOUND_BALL_GENERIC_PICKUP1,SOUND_BALL_GENERIC_PICKUP2,SOUND_BALL_GENERIC_PICKUP3,SOUND_BALL_GENERIC_PICKUP4,SOUND_BALL_GENERIC_PICKUP5,SOUND_BALL_GENERIC_PICKUP6,SOUND_BALL_GENERIC_PICKUP7,SOUND_BALL_GENERIC_PICKUP8,SOUND_BALL_GENERIC_PICKUP9,SOUND_BALL_GENERIC_PICKUP10"/>
 
  <sound event="bounce"       id="SOUND_BALL_GENERIC_BOUNCE1,SOUND_BALL_GENERIC_BOUNCE2,SOUND_BALL_GENERIC_BOUNCE3,SOUND_BALL_GENERIC_BOUNCE4"/>
  <sound event="land"         id="SOUND_BALL_GENERIC_STICK1,SOUND_BALL_GENERIC_STICK2,SOUND_BALL_GENERIC_STICK3,SOUND_BALL_GENERIC_STICK4,SOUND_BALL_GENERIC_STICK5,SOUND_BALL_GENERIC_STICK6"/>
 
  <sound event="attach"       id="SOUND_BALL_GENERIC_ATTACH01,SOUND_BALL_GENERIC_ATTACH02,SOUND_BALL_GENERIC_ATTACH03,SOUND_BALL_GENERIC_STICK1,SOUND_BALL_GENERIC_STICK2,SOUND_BALL_GENERIC_STICK3,SOUND_BALL_GENERIC_STICK4,SOUND_BALL_GENERIC_STICK5,SOUND_BALL_GENERIC_STICK6"/>
  <sound event="attachcloser" id="SOUND_BALL_GENERIC_STICK1,SOUND_BALL_GENERIC_STICK2,SOUND_BALL_GENERIC_STICK3,SOUND_BALL_GENERIC_STICK4,SOUND_BALL_GENERIC_STICK5,SOUND_BALL_GENERIC_STICK6"/>
  <sound event="detaching"    id="SOUND_BALL_GENERIC_DETACHING1"/>
  <sound event="detached"     id="SOUND_BALL_GENERIC_ATTACH01,SOUND_BALL_GENERIC_ATTACH02,SOUND_BALL_GENERIC_ATTACH03,SOUND_BALL_GENERIC_DETACHED1"/>
 
  <sound event="snap"         id="SOUND_BALL_GENERIC_SNAP1"/>
 
  <sound event="death"        id="SOUND_BALL_GENERIC_DEATH1"/>
  <sound event="deathfall"    id="SOUND_BALL_GENERIC_DEATH1,SOUND_BALL_GENERIC_DEATH2,SOUND_BALL_GENERIC_DEATH3,SOUND_BALL_GENERIC_DEATH4,SOUND_BALL_GENERIC_DEATH5"/>
 
  <sound event="suction"      id="SOUND_BALL_GENERIC_DETACHED1"/>
  <sound event="exit"         id=""/>
 
 
</ball>