That’s not at all what happened with the Demon Core. On its own, you could not do anything to it that would make it reach supercriticality. The experiments that were conducted on it involved neutron reflective materials. With the addition of neutrons back into the core, that pushed it closer and closer to criticality. Both incidents occurred when too much reflective material was added around the core and it reached supercriticality, a sustained chain reaction.
Kind of? It’s referencing a well known set of mass extinctions that are talked about together, the ‘Big Five’, but it also is worded poorly. Instead something like “Sharks have survived the most recent four of the ‘Big Five’ mass extinction events.” might be better?