For instance, Sephiroth, Fabled SOLDIER allows users to sacrifice a creature to draw a card when he enters the field or attacks
When tapped, it grants the player one blue or white mana per turn
The creature token that Mechtitan Core makes is very, very strong, and can provide 20-point life-swings while being incredibly hard to block or attack into
On the other hand, refusing to block would make World Shaper a cheap source of damage and self-mill each turn
As with cards like Fact or Fiction, your opponent has control over the final result here, which means you need to be able to build two strong piles
It opens up different pathways for curation and deck construction allowing for more creative expression