As seen above, the two sides of the card follow: Sephiroth, Fabled Solider: Legendary Creature - Human Avatar Solider Whenever Sephiroth enters or attacks, you may sacrifice another creature
Well break this up into three categories: Sure Thing, Situational, and Sleeper Hit
Often you will use it to counter an equip effect and feel really jipped by not getting great value out of the card however when you are a control mage you have to do what you have to do and just having those extra options goes a really long way
Your opponent trades their Colossal Dreadmaw with Ojer Taq to kill each other in combat, its death trigger will bring the god back as Temple of Civilization, and the additional trigger from Teysa Karlov will do nothing because Ojer Taq is no longer in the graveyard
Just dont use them for tournament play as you could booted out and get banned from future events
You may notice that five of these six are currently featured in Standard, and three of those actually made their debut within the past 18 months