While big Angels tend to cost lots of mana, cards like Urza's Incubator , Pearl Medallion , Oketra's Monument and Starnheim Aspirant will definitely help get them out faster
In addition to this, if we expand our criteria to include three-mana clones, we also have to take into account Glasspool MimicGlasspool Mimic, Mirror ImageMirror Image, and, functionally, Phyrexian MetamorphPhyrexian Metamorph
Its the same mechanic and restriction as Outpost Siege, but its a foil to several types of card draw, especially end-step card draw since any cards drawn can only be used on that end step
Plus, whenever another Creature dies, you get to put a +1/+1 counter on Ob Nixilis
The Summoner gives buffs to enhancement creatures (like Summon: Bahamut) with trample, lifelink, and ward (2)
On both faces, the other being Teferi Akosa of Zhalfir this card synergizes heavily with Knights