Just like Enchantments and Artifacts affect all cards in play (permanents), Enchantment Auras and Artifact Equipment cards affect a specific card they are attached to. Enchantment Auras can be applied to your opponent's card as a paralyzing effect. Artifact Equipment are usually attached to your cards via an equip cost. These two cards are great examples. Runchanter's Pike costs 2 mana to play and 2 more to equip and depends on the instant and sorcery cards in your graveyard.
Trepanation Blade cost 3 mana to play and 2 to equip and depends on the number of cards between mana in your opponent's library. It depends a lot on luck. I have played it and come up with one mana card (sucks!) but in some rare instances I have been able to get the +X to be X between 5 and 10, and I have put all of those cards in my opponent's graveyard.
