These force your opponent to discard a card from their hand, and while this might not appear all that powerful at first glance, repeatedly forcing your opponent to discard cards or being able to choose a specific card from your opponent's makes discard effects worthwhile
Dynamic composition, motion, and recognizable characters combined to create an instant classic
From the reminder text: "Tap any number of other creatures you control" is "tap any number of other creatures you control." "Or more" is "or more" (covered in #14), and "total" is "total," so: "With total power 3 or more" is "with total power 3 or more." Up to here: "Tap any number of other creatures you control with total power 3 or more" becomes: "Tap any number of other creatures you control with total power 3 or more." Since there is a ":" right after this, this part is the activation cost, making this keyword ability an activated ability
The payoff of transforming to Aang, Master of Elements is massive considering you already drew 5 cards (assuming you drew a card to start your turn)
I mean, weve come a long way since the days of giant, pricey monsters like Mold Demon and Minion of Tevesh Szat