Original Ben 10
A lot of red charcoals cover Ben's whole body, and then Heatblast is revealed. Similar to Four Arms, Wildmutt, and XLR8.
Muscular skin covers Ben's whole body, and two more arms pop out below his two normal arms, and then Four Arms is revealed. Similar to Heatblast, Wildmutt, and XLR8.
Muscular skin covers Ben's whole body, and then orange fur grows in his body, claws come out, revealing Wildmutt. Similar to Four Arms, Heatblast, and XLR8.
The diamond skin covers the arm, and then covers the body and face, revealing Diamondhead.
Skin of Ripjaws covers the arm, and then a huge antennae grows on his face, marks grow on the neck, inside the mouth teeth grows huge, Ben's skin and hair turn green and reveals Ripjaws.
Ben's face turns horrifying. The camera goes into Ben's eye, and revealing Ghostfreak's robe, revealing Ghostfreak's eye, and then shows its body.
Muscular skin covers Ben's whole body, feet turn into XLR8's feet, revealing XLR8. Similar to Four Arms, Heatblast, and Wildmutt.
Upgrade's skin covers Ben's whole body, revealing Upgrade.
Ben's body inflates like a balloon, and then the body turns into Cannonbolt's body, revealing him.
Vines cover Ben's whole body, and Wildvine's eye shows up, revealing Wildvine.
Grey Matter's wrists cover Ben's both wrists, and then a big Omnitrix symbol reveals on his back, and then the face and eyes turn into Grey Matter's face, revealing Grey Matter.
Stinkfly's arm cover Ben's arm, then four eyes of Stinkfly come out of Ben's face, which also makes a mark on his chin shaped like a beard. Wings and legs grow on his back, Omnitrix symbol shows up, revealing Stinkfly.
Personally, the transformation sequence looks too simple, it is mostly different skin covering Ben's body.
Ben 10 Alien Force/Ultimate Alien
Ben's arms to the waist grow Jetray's wings, Ben's hands and skull turn into Jetray's hands and head, revealing Jetray.
Ben's ribs grow some crystals, the skull changes into Chromastone's head, the back sticks out four crystals, revealing Chromastone. Similar to Diamondhead.
Ben's ribs grow some diamonds(Same part as Chromastone), the skull changes into Diamondhead's head, the back sticks out two long diamonds, revealing Diamondhead. Similar to Chromastone.
Ben shrinks down, and ribs shrink, revealing Echo Echo. Apparently the opposite of Swampfire.
Ben shrinks down, feet change into Big Chill's feet, shows eyes turning into Big Chill's eyes, revealing Big Chill.
Pieces of Lodestar's body assemble his arm, and then the arm does not show, and the assembled pieces turn into Lodestar's body, the head comes out, revealing Lodestar.
Ben shrinks down, and ribs grow, revealing Swampfire. Apparently the opposite of Echo Echo.
Ben shrinks down, eyes changes into eyes of Four Arms, arms split up into two each, and arms get big, revealing Four Arms.
Ben's arms turn into Brainstorm's pincers, and then the skull grows big, revealing Brainstorm.
Ben's skull, arms(including the Omnitrix), and then all of the body melts and turns into liquid. The liquid body slowly rises back up by the anti-gravity projector, revealing Goop.
AmpFibian's skin completely covers the whole body and face, then two stinger-like things come out of his body, revealing "AmpFibian"(with Ra'ad's eyes). This is the only sequence where it shows Ben's body with no silhouette.
Roughly similar to AmpFibian transformation in Fused, but shows Ben's body with black silhouettes.
Ben shrinks down, Armodrillo's metal plates cover his shoulders and arm, and the helmet covers Ben's face, revealing Armodrillo.
Going through Ben's body with space background with it, it shows a space background with a green planet, which it looks like it is going to blow up. Then, it reveals Alien X.