This will vary depending on the size of your needle and beads
Although the Dinosaur token enters the battlefield attacking, it was never declared as an attacking creature (for the purposes of abilities that trigger whenever a creature attacks, for example)
Mana Confluence + City of Brass Paying 1 life for a mana is a lot, but Mana Confluence and City of Brass make it worthwhile for perfect fixing
The history of Slivers in Magic stretches from their initial appearance on Rath in Tempest to the overlaymergingof Rath onto Dominaria during Invasion block, to their revival by Riptide scientists during Onslaught block, to their distant descendants surviving as the plane of Dominaria was dying during Time Spiral and beyond
Outside of that, it's a solid inclusion in any of the Draft formats where it's available (Cube, Ikoria , and March of the Machine )
So this is actually strictly worse than Gravedigger unless you are building some kind of rogue tribal deck