Look at Noelle or the Bitch epilogue chapter for what a shard does when it's really unleashed - depending on the host, the nature of the unleashed power can vary, specializing as it develops toward a task/specific implementation.
Grue's power would just spew darkness out in very direction to pretty much blanket and isolate an entire city, his body would become a vehicle for the power, and he'd mutate, quite possibly turning the 'tap into other passengers' ability into a link to just absorb power. Broken/dead shard, he'd continue doing so until those passengers lashed out, creating isolated, power-based effects/chunks of Grue in the midst of the city.
Tattletale's power would just scale up constantly in power, reach, and intensity of detail. The shard might not have broken 100% clean - Scion might have given it some tools somewhere in there, so I can imagine a Tattletale-sub-entity scaling up to a breaker state or tapping into a tinker ability to network/develop more hardware/brainware to process it all. Scale up to processing multiple dimensions at once, and develop/manifest/obtain a weapon. Going back to the tools Scion gave, a simple blaster power with a clean, possibly invisble terrain-penetrating laser, with Full-bore-tattletale focus at work to discern the best possible weak point? Or even just a Tattletale in the middle of it, holding a gun? Picture her systematically picking off threats one after another, from highest priority to lowest, from the center of the incident sites, maximum range.
Basically, you unshackle, the power scales up, the mind/body start to break down, and if the host is lucky, the shard can provide some means of housing the new data and form.
Standalone, without a host, the manifestation for the shard itself confronted in its own world, would be very similar in execution.