I imagine something akin to this might be what you're after. Much more in the way the sparkles are formed and travel, plus more mesh building, e.g. to form a pair of large boots from the ground up, could be added to enhance the overall effect.
Combining this with @Wossname's answer would enhance things also.
The main objective of this answer however, that of re-clothing your character from the feet up, is to demonstrate another relatively simple method of achieving this in Blender.
The exercise is performed in Blender's 3D Window, (stage) using a 3D model. You can use the same technique just as well with flat 2D drawings instead. (textured 2D planes)
The model (or drawing) of the character in normal clothing is in layer one. The zap-dressed model/drawing in layer two.
The secret is to have both models/drawings with EXACTLY the same dimensions so no change apart from the clothing would be noticable.
Blender will do this by duplicating layer 1's model, and moving the copy to layer 2.
The duplicate would then be allotted it's own exclusive material slots which would be textured this time with the hero's costume. Additional mesh for the boots & gloves would be added in this layer also.
In the case of 2D drawings, the first drawing plane would be duplicated in layer 2, so you'd need to retexture that with a modified drawing showing our hero with new clothing.
To keep both drawn characters at exactly the same dimensions, both would probably need to be produced in the same application that drew it in the first place.
i.e. Create a second drawing layer by duplicating the first, then repainting the clothing onto the copied drawing.
You would have two drawings, one in each layer.
Export both as separate image files with which to texture the two 2D planes in Blender.
Now for the zap!
Both layers would be included in the final render but layer 2's model or drawing wouldn't be visible initially.
An 'inviso' mask is used to do this in the second layer.
When the mask is slid upwards in the z axis, it would progressively unmask (reveal) the new clothing.
The original drawing would be masked in reverse. i.e. another 'Inviso' mask in layer 1 would rise from the ground up and progressively hide the original drawing or 3D model.
Both masks rise together and at the same speed to -
a) From the feet up, progressively render as invisible, the normally dressed character.
b) From the feet up, progressively reveal the zap dressed character.
Once the first model is hidden it can be instantly disposed of.
Animating limbs during this process is no problem because when duplicating, the copy inherits the original's keyframes. Synchronization is automatic -
Layer one's mask is positioned so it's top edge just overlaps Layer 2's mask lower edge so there would be no gap.
Sparkles (particles) could be added where the two planes meet. This one is parented to the Layer 2's Inviso. As it rises the view alignment changes so keyframed adjustments to the sparkle emitter's Z axis "location" will be necessary to correct this.
Alpha layering the final clip is also handy for making promos/demos. Inviso masks work just as well with this process.
Note how once alpha layered, our char can be sparkling into his uniform whilst placed 'physically' within this jpeg image, using (again) inviso masks, one for the chair, the other for the table to mask the shadow.
Inviso Masks - (Edited - New link 22/March 2019)
For details on how to create these, click here - How to put a mask into 3d space
NOTE: Inviso's will only work when rendering using "OpenGL". (Top left of window under "Render") PLUS everything must be deselected. i.e. Press 'A' before viewing or rendering. Also select "Only Render" in the 3D windows properties panel-->Display. (Press N)
A Blend file for this answer isn't possible in it's present form for reasons of copyright, (The 3D model)
The char has been replaced with a cube etc. To view it properly switch to the CAMERA VIEW. You can download the modified Blend file here -