You can't choose card types (e.g., artifact), supertypes (e.g., snow), or noncreature subtypes (e.g., Aura)
Its easy to set up delirium in decks that want to, and you can have a win condition based on the number of spiders you have, making Iskkanah a solid delirium commander
Umori, the Collector Choosing creature with Umori, the Collector makes all of your rats cheaper to cast, making it a natural commander for Rat Colony
Bringer of the Blue Dawn, for example, was recently discovered to be one of the previously added Momir cards thanks to a recent Reddit post
Besides giving you twice as many tokens as youd normally give yourself, this plays well into any of the councils dilemma or will of the council effects you can slam into a Tivit deck
Dinosaurs are great, but since they support each other, they tend to thrive when the deck is full of great dinosaurs