// Rot Farm Skeleton can't block.
this.addAbility(new CantBlockAbility());
// 2{B}{G}, Put the top four cards of your library into your graveyard: Return Rot Farm Skeleton from your graveyard to the battlefield. Activate this ability only any time you could cast a sorcery.
Ability ability = new ActivateAsSorceryActivatedAbility(Zone.GRAVEYARD, new ReturnSourceFromGraveyardToBattlefieldEffect(), new ManaCostsImpl("{2}{B}{G}"));
ability.addCost(new PutTopCardOfYourLibraryToGraveyardCost(4));
this.addAbility(ability);
}