Cresting Mosasaurus operates more like a sea monster (leviathan, octopus, kraken, or serpent) than a dinosaur, since it's a big monster that sends creatures back to your opponents' hand
If you want a value-oriented mono-black commander, you have much better options, from Gonti, Lord of Luxury to K'rrik, Son of Yawgmoth
All three of these cards are borderline, based on Wizards 's definition of epic and legendary
Now if this made tokens or had an ongoing sac outlet on it then I would be all over it but as it stands I think it is a card more suited to a Hecatomb deck as a backup powerful thing to do with sacrificial chumps
Learn how to play with your own deck, easy-to-follow rules, strategy tips, and reference card 100 CARD BLACK-RED DECK: With the Chaos Incarnate deck, embrace the chaos of war with the demon berserker Kardur, Doomscourge, and overwhelm foes with a multiplying army FOIL-ETCHED LEGENDARY CREATURE CARD: Includes 1 legendary creature card with gorgeous art and a foil-etched treatment
Temple is more exciting on its surface, and Im looking forward to digging deeper