In the old days, the baseline for mana rocks was to actually produce mana the turn they came into play, like Mana Vault, Mana Crypt, the Moxen, and Grim Monolith
This was printed at a time where Settle the Wreckage was popular in Standard, and that sentiment follows in Commander so long as Spellbreaker stays on offense
The current plane goes to the bottom of the deck
Then, a second "reflexive" ability triggers (denoted by the phrase "when you do") that requires a target
When working with the typal theme, one of the design team's goals involved finding more ways to get typal cards that aren't creatures into a typal deck
Each one is either an instant or sorcery with an X in its mana cost, and that X can be paid for by exiling cards of the corresponding color from hand