That said, you can win without your commander, and while that's easier to do after Yidris has dealt damage to an opponent, the deck is more than capable of winning without it
For a measly one mana, its a pretty good enabler
Normally it ties four- or five-color decks together, but there are constraints on Pioneer we havent had to live with for a long time
Every time that you cast a noncreature spell, you can flicker a nonland permanent that you control
A poor (dare I say obstinate) familiar can impede spellcasting and limit new discoveries, while an excellent familiar like Kediss can enable spellcasting of incredible scale
Being able to deal a big hit of damage when he dies is fun, too