WMG / Smosh

No special effects were used at all in their videos.
What? This is WMG, after all. I do have a small theory on just how this is possible...

Which is...
These guys live in an Alternate Universe or a Pocket Dimension where most tropes (like Death Is a Slap on the Wrist, Reality Ensues and Rule of Funny) all apply to them...
Most likely the Internet.

The birthday cake in "PARANORMAL EASY BAKE OVEN!" was made out of several smaller cakes
With icing coated around it to make it look like it was one large cake, explaining how the Easy Bake Oven could make a cake larger than it.
http://tvtropes.org/pmwiki/pmwiki.php/WMG/Smosh