Does the 6th level ability Malleable Illusion mean I can animate an illusion?
For example, if I make an illusion of an animal or a party member, can I use my action to make that illusion look like it is walking/acting in a way that is natural for a 'real' creature?
Or, does it mean that once every 6 seconds I can suddenly change it from one thing to another?
Thanks 
I believe it means you can change what the illusion is.
Some illusion spells (Minor Illusion for this example) allow you to create a creature an object such as a chair or door. This level 6 feature could mean you could change the door to a brick wall without needing to recast the illusion. The door would simply morph into a wall.
Silent Image lets you create the image of a creature (among other things) and animate and move it like it would a normal creature of its type. I think this feature allows you to change the creature to a different creature entirely, once again without needing to recast the spell. So the image of a wolf stalking can suddenly change to that of a motionless gargoyle or something like that.
So, to shorten it a little, I'm pretty sure the Malleable Illusion feature allows you to change the image you are making with your spell to something completely different (but still within spell parameters) without needing to cast the spell all over again and waste spell slots.
Ah, so any 'animation' ability must be included in the spells discription.
Gotcha, thanks!