I want to make the polar bear look like it is eating santa! But the santa I found off the internet! How do I make it disappear when it is touching the polar bears mouth???

Simplest is to use a Hide block.

forever
    Simplify
end

If you want it to hide only when it touches the mouth, instead of touching anywhere on Santa, you will have to do something. Santa's mouth can be a different color and you can use

<touching color [#f0f]?>

You can have a small sprite that stays fully ghosted, not hidden. This sprite must always goes to where Santa's mouth is. The requires math or trig or something. You can then use

<touching [Mouth Sprite v]?>