almost any card can be used as Ink, which solves the problem of not having enough Energy, as in Pokemon, or Mana, as in Magic: The Gathering
Its an important choice, and one that should be carefully considered, but it is a choice that I believe should always be made
If you are already playing tutors, you can treat graveyard hate as a silver bullet suite instead of raw density
On the other hand, Theater of Horrors is generally a better Outpost Siege, since you have more time to play your exiled cards, though Siege does have the added flexibility of being able to be played as a win condition in Purphoros, God of the Forge decks and similar Go Wide decks
This Teach card has a cost of 10, meaning it wont make it out on your field until late game unless you can cheat extra DON