These cards are worded specifically to bend the rules of Magic, letting you play as many of them in your deck, with a bonus or two for having more of them in play or having played them during a game
Typal decks are really popular, especially in Commander, so WotC is always releasing new typal cards to strengthen the existing archetypes or to create new ones entirely
As long as someone just died, of course
How does a zombie deck win
Then, something like [c]Past in Flames[/c] will give them all flashback, so you can cast each one of them a second time
Sigarda, Herons Grace Sigarda, Heron's Grace gives you and humans you control hexproof, and that can be exploited in human tribal decks