Even a relatively tame set of instants or sorceries like Pongify, Serum Visions, and Faithless Looting can completely lock down a game while searching your deck for whatever card you need
Fischer, meaning if you build an Angel deck around the #13 overall commander on EDHREC, and the #1 Angel commander by far, youll have a fairly unique and truly beautiful rendition of this two-drop legendary Angel
Worldly Tutor can find either Sprouting Phytohydra or Scourge of Valkas, getting whichever piece of the combo you're missing into your hand
Old One Eye Something something big dumb creatures oh wait, Old One Eye is a big dumb creature and creates another big dumb creature when it enters, can buy itself back later in the game, and gives all of your creatures trample
It also gains the activated abilities of whichever goblin rests atop your humble deck - which means that it can serve as an extra copy of whatever you want it to be, without having to invest the mana first