You have to be careful with what you're copying, as you don't want to waste mana on creating a copy instead of casting the permanent
One of the nice things about Piledriver is that even when you can't force him through he will at least force through and pseudo protect all your other valuable utility goblins as they will simply be forced into blocking Piledriver to not die
There's a bit of a cute idea here, with the deck attempting to play prototype creatures for cheap, then either blink them or recur them with Fake Your Own Death to plop them back into play on their fully upgraded side
2 Vorinclex, Voice Of Hunger Vorinclex, Voice of Hunger is a Phyrexian Praetor creature with inverse abilities, like Jin-Gitaxias
So, three mana for a buff and cost reduction comes out at a pretty decent rate
Id certainly pay four life to have repeatable Solemn Simulacrums every turn