Basically (because I know the wording of the attack might sound confusing), you have a 50% of dealing 150 damage to each of your opponents Pokmon on the field
They can be used in good faith, or for ill, and the verdict on how problematic a card can be is more complex than whats written on it: it requires context of how and when its played, with what cards it is played, and in what scenario
The SAR slot alone contributes 3,044 (34%) of total box value
Once in play, Cavern of Souls can be tapped for one mana of any color, but there's a catch
Concealed Courtyard, Spirebluff Canal, Blooming Marsh, Inspiring Vantage and Botanical Sanctum reprint MTGs offering of enemy fast lands - land cards that can be tapped for either of two mana colours, but enter the battlefield tapped unless you control two or fewer other lands