One popular thread on the topic (source) highlights: Pull rates for SIR cards are approximately 1 in 68 packs
His ability is great as he wont take damage back unless you use him to challenge instead

Tymna the WeaverTymna the Weaver Ragavan, Nimble PilfererRagavan, Nimble Pilferer Purphoros, God of the ForgePurphoros, God of the Forge Kinnan, Bonder ProdigyKinnan, Bonder Prodigy Winota, Joiner of ForcesWinota, Joiner of Forces Azusa, Lost but SeekingAzusa, Lost but Seeking Jodah, the UnifierJodah, the Unifier Muldrotha, the GravetideMuldrotha, the Gravetide Gix, Yawgmoth PraetorGix, Yawgmoth Praetor Kraum, Ludevic's OpusKraum, Ludevic's Opus Ishai, Ojutai DragonspeakerIshai, Ojutai Dragonspeaker Bruse Tarl, Boorish HerderBruse Tarl, Boorish Herder Adeline, Resplendent CatharAdeline, Resplendent Cathar Inalla, Archmage RitualistInalla, Archmage Ritualist Godo, Bandit WarlordGodo, Bandit Warlord Sram, Senior EdificerSram, Senior Edificer Varragoth, Bloodsky SireVarragoth, Bloodsky Sire Mangara, the DiplomatMangara, the Diplomat Loran of the Third PathLoran of the Third Path Venser, Shaper SavantVenser, Shaper Savant Of course, all this means nothing if you're really, really excited to get your hands on the Final Fantasy'd version of your favorite commander

Compare this to the other green creature tutors in the format and this becomes clear
Just looking at my two Zombie decks (Gisa and Geralf Together Forever and Zombies of Tresserhorn), there are some saucy choicesamplified by the fact that theyre Zombie decks, so theres a pretty good chance that the sacrificed creature is coming back anyway