Cataclysm has three distinct, separate uses.
1) It keeps your opponent from getting too close to having six unrazed realms. This is self-explanatory I would think.
2) It can be used to remove from play a land that you yourself have in your hand, allowing you to place it into your formation. Because the Rule of the Cosmos forbids two of the same realm from being in play simultaneously, and razing it doesn't get around this, the Cataclysm comes in handy.
3) It can be used to remove a land with a particularly onerous movement restriction or other power. Don't like the look of that Raurin out front in your opponent's formation? POW! All gone.
Events are as a rule harder to stop than spells, so Cataclysm has a leg up on cards like Disintegrate and Raze. Cataclysm works on lands that are razed or unrazed, which puts it ahead of Dissolution and Creeping Doom. Estate Transference is arguably better, since it places the enemy realm in the more inaccessible Abyss instead of the easier-to-retrieve-it-from Discard pile, but Estate Transference can also be Dispelled easier.
For my money, the best way to cause your opponent to feel the wrath of a natural disaster is still Cataclysm.
Next Time: Retarget and Deflection...overrated cards?
