Your creatures are going to be sacrificed left and right so youll have lots of opportunities to do this. Shes a survivor, too: at any time, you can sacrifice a creature and pay one mana to make her indestructible until the end of the turn, like shes using its corpse as a shield
Even if you just tick it down to force some sacrifices and draw cards, thats killer on certain board states
Then, it has both trample and hexproof, ensuring that at least some damage is going to slip through your opponents defenses, and making it awfully difficult to remove outside of combat
Its token production pairs perfectly with merfolk lords to create a board that goes very wide, but also pretty tall since more merfolk makes Namor larger
While the Legions original is the collectors choice, even the Commander 2014 reprint is seeing intense pressure as supply vanishes from major platforms