After the next rotation, you arent going to replace Dragonlord Ojutai with Archangel Avacyn and Silumgars Scorn with Broken Concentration
Theres the usual balance considerations of other formats, but also things like whether or not a card promotes unhealthy play patterns for a four-player casual format
For example, if a single-faced card is a copy of The Legend of Kyoshi, the chapter III ability will cause it to be exiled and then remain in exile
Creature - Goblin Warrior Color tag templates(None) Kiki-Jiki, Mirror Breaker Haste : Create a token that's a copy of target nonlegendary creature you control, except it has haste
Its often the ultimate companion piece for plenty of outstanding partner commanders who can draw into it or cheat it out, and is essentially the final boss of blue magic that can turn every card in your hand into an unstoppable threat
It still adds some personal flavor too, using typefacing and a Phyrexian to get the point across