These cards required three sacrifices in order to be summoned, and each of them had unique abilities that could swing the match in favour of the player who summoned them
Since you dont have a lot of it, your instant-speed removal should be reserved for the direst of threats
Plasm Capture would have been a whole lot better at 3UU to cast and Spell Swindle is a whole lot better than Plasm Capture regardless of cost
Three mana to cast Varragoth, 2 mana for each boast activation to put your combo pieces on the top of your library, and then Sickening Dreams to deal a ton of damage to a player or creature (probably a player)
If you don't, no ability will trigger, and it will untap normal during your next turn
As the library expands with these massive sets, collectors often take stock of the history to find out how many MTG cards are there in existence