Like most Magic: The Gathering cards, the value of Mortarion, Daemon Primarch depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Warhammer 40,000 Commander)
Pendulum Storm X SPELL Destroy as many cards in the Pendulum Zones as possible, then you can destroy 1 Spell/Trap your opponent controls
The effect is also top class among level 6 synchros
Dragonlord Atarka could stabilize your board by taking out a creature and being a 8/8 blocking body, but her board presence is less resilient than Hornet Queen
It's also important to read their pattern listing too if you are purchasing to see whether they are for personal use or also for commercial use
Thats why I made this guide: to help you find the perfect binder that balances style, protection, and quality