If the heart stops, it will die
Level two, giving your whole board menace, is pretty nice, and can be a pretty big problem on a lot of board states, but level three is where the real value can be found here, as getting to cast cards you exiled with Rogue Class is going to be quite powerful
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Amber is king of singing Rise of the Floodborn introduced several powerful characters with the Singer ability, further emphasizing Ambers distinction as a deck thats great for signing songs to gain an advantage over your opponent
Its also worth noting that the tap ability doesnt care about summoning sickness, so instant-speed creatures can do their part
See rule 309, Dungeons. 309.1: Dungeon is a card type seen only on nontraditional Magic cards