If you already have these Gaster Blasters not only as floating heads but as whole creatures, who says there can't be kids versions as well?
These cuties are around 30 cm large as kids and very light, but they can grow up to 2 metres as adults.
Due to their fishbone structure their bones are connected like magnets - they can float and rearrange within a short radius and that's perfectly normal (you can see it on the last segments of the tail) because otherwise their head wouldn't be very moveable.
Usually you can see their inverted heart through the chest, but on these pictures I'm too lazy to draw them xD
Also, have a small sketch of the Baby Blasters.
(Oh, and unlike the Baby Blaster brothers the Pet Blasters are creatures like dogs or cats, just much stronger)