Each Dragon is looking forward to dealing combat damage to your opponents, and each is available in a borderless version
Source: Mythic Spoiler OpenCritic Reviews Top Critic Avg: 82 /100 Critics Rec: 82% Released September 27, 2018 ESRB T for Teen // Blood and Gore, Mild Fantasy Violence Developer(s) Wizards of the Coast, Wizards Digital Games Studios Publisher(s) Wizards of the Coast Engine Unity Multiplayer Online Multiplayer Franchise Magic: The Gathering Platform(s) PC, Android, iOS Genre(s) Digital Card Game
If you care then Fellwar Stone is going to be very unreliable and if you don't then you have marginally better options
The more mana you have in early turns, the faster you can play spells and creatures, and start building up your board
In this sense, Horn of Valhalla both acts as a way to develop your board and as a payoff once your board is developed, which is quite powerful