1 DARK Tuner + 1 or more non-Tuner Fiend-Type monsters Once per turn: You can banish 1 Level 6 or lower DARK Effect Monster from your Graveyard; until the End Phase, this card's name becomes that banished monster's, and replace this effect with that banished monster's original effects. If this card is destroyed and sent to the Graveyard: Add 1 "Earthbound Immortal" monster from your Deck to your hand.
Hundred Eyes Dragon copies the effect of monsters in your graveyard so you need a way to get your DARK effect monsters to the graveyard. Since many Zombie monsters are DARK attribute, Gozuki and Samurai skull can get them into the graveyard. You can also use these cards to mill the top of your deck and hope you put good effect monsters into your graveyard.
Here are some level 6 or lower DARK monsters with good effects you can copy. Copy the effect of Mucus Yolk, Jinzo Returner or Jinzo #7 to attack your opponent directly with your 3000 attack. Jinzo prevents the activation of trap cards for the turn. Copying Archfiend Giant protects Hundred Eyes Dragon from being destroyed once.
No, it will be Ccapac Apu. He said it himself if you destroyed Hundred Eyes Dragon, that the Earthbound Immortal is the ace card of the Dark Signers, so Ccapac Apu will be his signature card even in DL.
Starter deck will likely contain Ccapac Apu, and Infernity Doom will be his "Signer __" skill, with Hundred Eyes being his event card.
Since Hundred Eyes doesn't have a summoning animation, it's more likely that either Ccapac Apu or InfDra has the animation, if not both.