It's a game-ender, typically sweeping away your opponent's entire board, while preserving any colorless permanents you've chosen to play, and, more often than not, also leaving Ugin alive to keep pecking away with their +2 damage-dealing power
However, although ultimatum is the dictionary meaning of Ultimatum, in reality, it is closer to Ultimate , which takes Ultimatum as its etymology, and is much more in line with the characteristics of the card than viewing it as an Shards of Alara is a card from the block Shards of Alara and Ikoria: Lair of Giants
Over the past few months, it seems players have really woken up to this fact, resulting in the cards price almost doubling
That said, the exact combo of Starnheim Unleashed and Battle is a bit on the win-more side except in midrange mirrors