If I copy a Pentad Prism with a Sculpting Steel (using, say 3 different colors of mana), does the Sculpting Steel come in to play with 3 charge counters, or zero due to some weird Sunburst/copy rule?
You get 3 counters. It used to be different, but they fixed it to be more intuitive.
One more question (sigh...), if someone has Grip of Chaos in play(The enchantment that makes all targets random targets), and I want to Weld an artifact in play, what happens? Assume both players have artifacts in play and in the graveyard. Does the welder first randomly target an artifact in play, then randomly chooses an artifact in that player's graveyard to swap for?
Read the card.
Grip of Chaos


{R}
Enchantment
Whenever a spell or ability is put onto the stack,
if it has a single target, reselect its target at random. (Select from among all legal targets.)