Boromir is also cheap enough that if you need to sac it, you can easily recast it soon
Valakut, the Molten Pinnacle's triggered ability has an "intervening 'if' clause." That means (1) the ability won't trigger at all unless, at the time a Mountain enters under your control, you control five or more Mountains other than that new one, and (2) the ability will do nothing if you control fewer than five Mountains other than that new one by the time it resolves
With Kardur, Doomscourge be patient enough to let your opponents play down some heavy hitters then you get maximum impact from the ETB that goads all opposing creatures
Value is basically the name of the game
First things first, its worth noting again that Battle cards can be damaged by more than just combat damage from creatures
There are some color-matching requirements in the game, so Sealed has just enough variation to make it a repeatable and unique experience each time