I'm really enjoying this set so far which is full of "What would a Vintage staple look like if we didn't mess up the design the first time."
This is the best example. Costing 2 and having an activated ability of 1 is strong, but reasonable. And Welder, nor the color pie or abilities in general, are meant to just permit exchanges in the opponent's graveyard.
That said, I would have never thought of adding a built-in Entomb, and I think it's great flavor!
@blindtherapy It's also a bit more restrictive in the case of a topdeck situation where you don't already have the extra card to pitch, meaning you can't remove the threats right away and then attack or cast more stuff. If you don't have a big density of green cards, this should come up quite often.