In that case you cannot make them in webflow natively as far as I can tell, though I remember @vincent posting a sort of tutorial to something similar, maybe he will remember.
Otherwise you will need to insert custom code from someone’s pens to your liking like this or this or this. Basically just search “blob” on a codepen to see if there is anything you like in particular.
Refer to these resources on how to use custom code in Webflow.