The “Shockland” effect of entering play tapped unless you pay 2 life is not a trigger (you can tell since it doesn’t contain “When ~ enters the battlefield”). Rather, it modifies how the land enters the battlefield in the first place. This ability still happens even with Blood Moon in play, since Blood Moon only modifies lands in play, not ones in hand.
In short, Player A’s Temple Garden entering the battlefield with a Blood Moon in play gets to choose to put it into play tapped or untapped (by paying two life), because the replacement effect has to apply before it actually enters the battlefield under the effect of Blood Moon. But once it’s on the battlefield, it only taps for R, since Blood Moon modifies the land type from ‘Land – Plains Forest’ to ‘Land – Mountain’. Also note that it’s NOT “Basic Land – Mountain”, so Price of Progress or Tectonic Edge would still count it as a nonbasic land.
Today’s Rules Tip written by Eddie Cheung