Rhinestone hotfix Art, you can create design as what in our own mind, DIY gift set for teacher, mask for party, decoration of clothes, 3d model, mobile case, young children and adult will like this interesting art, I guess.
Two method of doing this Art.

Method 1 : use Hotfix wand on irregular shape of un even surface workpiece, such as hotfix on fabric
Shoes, my 3D cardboard house etc.

Method 2: use transferring sticker paper on flat surface which can iron, such as clothes, tee-shirt, pants etc.

Not all mobile case suitable for hotfix, check it material first.