When mana is often the largest chokehold in competitive Commander games (which is a topic I could write an entire article about someday), Dark Ritual is the best of many options for making a lot of mana very quickly
If you have a haste enabler, the Valkyrie will be able to tap once again to put her protection on Gerrard, allowing you to clear the board again whenever you get the chance
Loads of walkers plus pumping the other zombies you might have
Even for the same character, the price difference becomes extremely large depending on specification variations
If you have a lot of decks like that in your local playgroup, you can take advantage of the End the Turn part of Ultima to stop things happening after it resolves
VSTAR Power Ability: Star Portal During your turn, you may attach up to 3 [W] Energy from your discard pile to your [W] Pokmon in any way you like