At a CMC of 4, Bloodbraid Elf allowed Jund to cascade into basically any card in its deck
Some decks struggle with a cheap indestructible creature while the combat trick works against just as many decks
Even the engine combo decks in cube tend to have sufficient overlap or utility from other combos in the cube to double up
If you want to stop someone from getting a Clue token, you have to counter the spell or ability that causes them to investigate in the first place like countering an Expose Evil, or using a stifle effect like Disallow to stop a triggered ability that would make a player investigate
Fetchlands and fetchable duals, particularly Triomes, enable players to play three or more colors, whereas shocklands, fastlands, painlands, and any land that enters the battlefield tapped while only tapping for two different colors will push players to draft more two- to three-color decks