The sixty cards each player has drafted form their "draft pool." Using those cards (and as many basic lands as desired), each player builds a deck of at least 60 cards, including their commander
10 Tricky Terrain Everything On Anything One of the Modern Horizons 3 Commander Precons, Tricky Terrain was all about putting everything counters on your lands and creatures
Entering the battlefield with two additional bodies is slight overkill for Celebration triggers, so this card is most efficient for Rat sacrifice builds and might get bulked up into a semi-evasive finisher, something every "aristocrat" deck needs
Any colored mana costs must be paid by the spell's controller, even if the assisting player paid mana of that color
Besides these two, Golgari Charm , Culling Ritual , and Find/Finality provide both utlity and slightly more situational mass removal
In general, blue is associated with control, and in particular, countering and milling