When it comes to doing a quick and dirty expected-value calculation of your own, the formula is the same for rares as for mythics: add up the value of all of the rares in the set, divide by the total number of rares in the set (almost always 53), and then multiply by the number of rares you should open in a box (31.5, with the other 4.5 rare slots being filled by mythics)
For two Energy, it does 20 damage and allows you to flip a coin
Altar of the Brood simply makes it so that each permanent that enters the battlefield under your control causes each opponent to mill one card
TRADING CARD GAME Tournament Policy and the Official KDE-US Tournament Infractions and Penalties Policy documents
You cannot normally cast things in your color identity, but with this, you can cast your foe's card draw, like Mulldrifter with evoke or Esper Sentinel
So, Gloom Pangolin taps and attacks