The Bone Goo Ball is extremely resilient. It cannot be destroyed by spikes, so you can use it protect other balls.

<ball
  name="Bone"
  shape="rectangle,50,50"
  mass="60"
  towermass="4.0"
  strands="2" 
  walkspeed="0.1"
  walkforce="3000"
  climbspeed="0.9"
  speedvariance="0.2"
  jump="0.0,0.3"
  sticky="false"
  blinkcolor="0,0,0"
  invulnerable="true"
  grumpy="false"
  hingedrag="false"
 
  attenuationselect="0.05, 1.0, 1.2"
  attenuationdeselect="0.05, 1.2, 1.0"
  attenuationdrop="0.05, 1.2, 1.0"
  attenuationdrag="0.05, 1.2, 1.0"
 
  maxattachspeed="1000" 
  material="BoneBall"
 
  jumponwakeup="false"
  staticwhensleeping="true"
  >
 
  <marker drag="IMAGE_BALL_BONE_DRAGMARKER_P1" 
          detach="IMAGE_BALL_BONE_DETACHMARKER_P1" 
          rotspeed="2" />
 
  <shadow image="IMAGE_BALL_BONE_SHAD"/>
 
  <particles id="sleepyZzz" states="sleeping" overball="true" />
 
  <strand type="spring" 
          image="IMAGE_BALL_BONE_STRAND" 
          inactiveimage="IMAGE_BALL_BONE_STRAND" 
          springconstmin="10" springconstmax="10" 
          dampfac="0.9" 
          maxlen2="120"
          maxforce="800"
          minlen="100"
          thickness="20"
		  walkable="false"
		  />
 
  <detachstrand image="IMAGE_BALL_BONE_DSTRAND" maxlen="60" />
 
  <splat image="IMAGE_BALL_BONE_SPLAT1,IMAGE_BALL_BONE_SPLAT2"/>
 
  <part name="jaw"
        layer="0"
        rotate="true"
        x="0" y="-25"
        image="IMAGE_BALL_BONE_JAW"
        stretch="24,1.5,0.75"
        scale="0.76"
        state="climbing,attached,walking,falling,dragging,detaching,standing,tank,sleeping,stuck,stuck_attached,stuck_detaching"
        />
 
  <part name="body"
        layer="1"
        rotate="true"
        x="0" y="0"
        image="IMAGE_BALL_BONE_BODY1,IMAGE_BALL_BONE_BODY2"
        stretch="24,1.5,0.75"
        scale="0.75"
        />
 
  <sound event="drop"         id="SOUND_BALL_GENERIC_MUMBLE1,SOUND_BALL_GENERIC_MUMBLE2,SOUND_BALL_GENERIC_MUMBLE3,SOUND_BALL_GENERIC_MUMBLE4,SOUND_BALL_GENERIC_MUMBLE5,SOUND_BALL_GENERIC_MUMBLE6,SOUND_BALL_GENERIC_MUMBLE7"/>
  <sound event="throw"        id="SOUND_BALL_GENERIC_MUMBLE1,SOUND_BALL_GENERIC_MUMBLE2,SOUND_BALL_GENERIC_MUMBLE3,SOUND_BALL_GENERIC_MUMBLE4,SOUND_BALL_GENERIC_MUMBLE5,SOUND_BALL_GENERIC_MUMBLE6,SOUND_BALL_GENERIC_MUMBLE7"/>
  <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="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="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="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="suction"   id="SOUND_BALL_GENERIC_DETACHED1"/>
  <sound event="exit"      id=""/>
 
 
  <!-- climbing animations -->
  <sinvariance freq="0.3" amp="0.03" shift="0">
    <sinanim part="jaw"  state="climbing" type="translate" axis="y" freq="4.0" amp="3"   shift="0"   />
  </sinvariance>
 
  <!-- dragging animations -->
  <sinvariance freq="0.3" amp="0.03" shift="0">
    <sinanim part="jaw"  state="dragging" type="translate" axis="y" freq="4.0" amp="10"   shift="0"   />
  </sinvariance>
 
  <!-- dragging animations -->
  <sinvariance freq="0.3" amp="0.03" shift="0">
    <sinanim part="jaw"  state="attached" type="translate" axis="y" freq="4.0" amp="3"   shift="0"   />
  </sinvariance>
 
  <!-- tank animations -->
  <sinvariance freq="0.3" amp="0.03" shift="0">
	<sinanim part="jaw"  state="tank" type="translate" axis="y" freq="4.0" amp="3"   shift="0"   />
  </sinvariance>
 
</ball>