Especially since Eiganjo Dynastorian becomes prepared every time you attack with two or more creatures, you can cast this somewhat frequently as long as he doesnt die
We're in Green and Blue, so we've got access to the kind of land ramp that can make her playable, but we'll still get blown out every so often by a low mana aggro deck that can win earlier than we can even get things set up
Your opponents need to hit ten poison counters to lose and with Atraxa triggering at the end of every turn, that clock ticks faster than it looks
Some cards are natural buildaround cards, which are only good if you build your deck to maximize some aspect (sacrifice creatures, combat damage, spellslinger)
If the copied creature is a token, the new token that's created copies the original characteristics of that token, with the exception noted above