Xanthan, guar, and locust bean gum are to control melt and improve texture – many people add them to homemade ice-cream even.

Xanthan is the best if you need non-toxic slime for artistic purposes (e.g. Halloween decorations).

Just make a stiff gel and hit it with a stick blender for desired consistency and lumpiness. This does introduce a lot of small air bubbles in it, so if you need clear slime let it stand for a few hours.