Drogskol Captain: I like Lord effects. I really do. They make me feel warm inside. A Lord that boosts my creatures and provides Hexproof, thereby protecting them from non-combat-based threats. This card is central to boosting my creature base so that I am dealing the most damage possible. Well worth a 4-of.
Geist of Saint Traft: A 2/2 for 3 CMC with Hexproof that launches a token:4/4 Angel token into my opponent's face whenever it attacks. Also a Spirit which benefits from my Lord effects. He is an incredibly potent early-game threat, and well worth having three in the deck.
Mausoleum Wanderer: The Shadows over Innistrad block brought forth a generous supply of Spirits with which to attempt a worthy Spirit Tribal deck, and this creature is one of those additions. Its low mana cost of allows it to have an early board presence, but what makes this card great is its ability to scale with the amount of Spirits placed onto the board on a turn. Fortunately, every creature in this deck is a Spirit! This scaling also affects its ability to be sacrificed to counter instant/sorcery spells, allowing it to be a threat throughout a game.
Rattlechains: This is a must-have for this deck. Aside from the delivering of Hexproof on a given Spirit, which helps to cover the ass of Drogskol Captain, the ability to cast my Spirits as though they had Flash is monumentally helpful. This allows me versatile gameplay during both my turn and my opponent's turn. Being a 2/1 with Flying for 2 CMC is also great for offense. Not something I need four of, but three works just fine.
Selfless Spirit: I used to run the Kami of False Hope/Angel of Flight Alabaster combo in this deck, as it allowed for the consistent shutting down of an opponent's offense with creature. This combo, however, was clunky and could also prevent my own creature damage. This is no longer an issue with Selfless Spirit. This creature, when not serving as a decent threat in its own right, allows to be sacrificed to grant Indestructible to my creatures, granting a substantial boon to my offensive especially considering that most of my creatures have Flying.
Spell Queller: I originally had doubts about this creature, as I was skeptical of having the opponent freecast a spell should my creature die. Then I remembered that I have been a fan of Dungeon Geists for as long as I've played Magic, so I decided to throw these in. They have more versatility than Dungeon Geists, cost less mana, and can be Flashed in on their own without the help of Rattlechains. Overall, a wonderful card and a welcome addition to this deck.