In short, Shichifukujin Dragon was created to commemorate the opening of the DCI Tournament Center and 1996 World Champion is exactly what it says - the card was created as a prize for the winner of that tournament (Tom Chanpheng)
This meant that more and more players of all skill levels were starting to play with a greater number of four-of's in their deck
The mechanic is a variation of Ninjutsu , requiring either an assassin or your commander to deal combat damage during that turn for Freerunning to activate
Necron Dynasties is a Mono Black Artifacts deck with a strong Graveyard subtheme: the deck wants to fill your graveyard with artifact creatures either through self-mill with cards like Flayed One or sacrificing them with cards like Illuminor Szeras, then bring them back out of the graveyard with cards like Technomancer or unearthing themselves like Lokhust Heavy Destroyer
Solemn Simulacrum
Here, the 'cleanest' line of argument for plague themed cards being banned is: "MtG has plague themed cards, there is a current pandemic whihc is bigger than any other recent pandemic, I know somebody who died becuase of the pandemic, I'm angry at any reminder about the pandemic, ergo, I am angry at WotC for having cards which remind me of this." This is very clearly a stretch, as the same argument could be that the game in general depicts death and somebody might be upset about the death of a loved one (from a COVID unrelated issue)