I am at the checkpoint with the Welder and Gauntlez Gruntz. How do I get one of them to the green switch, over the spikez and back without dying?
You can't. The Rolling Snowball is supposed to do the work for you, I believe. (I may be confusing Custom Levelz, but I believe this is the case. If I am wrong, I will modify this post after I have checked it out.) Part of your problem is the distance between cause (Switch) and effect (something toggled). A large screen resolution will help a bit ... I use 1024 X 768, myself.
Edit: I just checked the Custom Level out, and it is the one I thought it was. Even 1024 X 768 is not large enough to see all of the Arrowz that get toggled by that Yellow Hold Switch (YHS); however, it does more than just release the Rolling Snowball (RS) near the YHS ... it also releases a RS in the spiky area. Timing is important; you must get through the Wormhole and do something to allow the second RS to do everything required for you to complete the CL.