Because so few perfect copies of these common cards exist, getting one graded creates a massive premium
If you didn't put any cards into your graveyard when you manifested dread (perhaps because your opponent controls Leyline of the Void), Paranormal Analyst's ability will still trigger, but you won't be able to put any cards into your hand when it resolves
Finally, speaking of lands, theres a special something about Battle for Zendikar that might appeal to the gambler in you
As for why the Rapid Strike Urshifu is three times as valuable as the Single Strike Urshifu
You only really want mana dorks early, ideally turn one and Mentor can't do that
Most Toxic creatures are only Toxic 1, such as the iconic Phyrexian Mite tokens -- although there are some fun outliers, like Tyrranax Rex, which has a brutal Toxic 4