A higher percentage is better
I'm thinking Battlegrace AngelBattlegrace Angel, Sovereigns of Lost AlaraSovereigns of Lost Alara, Sublime ArchangelSublime Archangel, as well as enchantments like Battle MasteryBattle Mastery, Duelist's HeritageDuelist's Heritage or Flaming FistFlaming Fist
As sagas, they are short-lived
The most basic and common of which is simply denying one attacker damage for a turn
As we see in Viral Spawning, this turns on the flashback portion of the card, giving you a slight discount from Call of the Herd at three mana

Synergy, Griefing, Staples, Building a Doran Deck ) My current Commander decks (and links to decklists) : Ruhan of the Fomori (lots of equipment and infinite attack steps) Phage the Untouchable (actually casting Phage from Command Zone!) Ghave, Guru of Spores (Melira Combo) Glissa, the Traitor (undying artifacts!) Previous Commander decks currently on hiatus : Grimgrin, Corpse-Born (Necrotic Ooze Combo) Damia, Sage of Stone (Ice Cauldron shenanigans) Geist of Saint Traft (Voltron-ish) Glissa Sunseeker (death to artifacts!) Jor Kadeen, the Prevailer (replacing Brion Stoutarm in Mo Myrs) Thelon of Havenwood (Campfire Spores) Melira, Sylvok Outcast (combo killa) Konda, Lord of Eiganjo (The Indestructibles) Vorosh, the Hunter (proliferaTION) Progenitus (Fist of Suns and Bringers) Savra, Queen of the Golgari (Demons) Uril, the Miststalker (my "more competitive" deck)