I lost the first game with a different deck, with too many 7+ spells and less sigils, which resulted in an awful starting hand. I changed the deck right after, and used the deck shown on this page for the following games.
I lost another game due to a stupid mistake in the last turn: I did not attack with every unit because I forgot "Adaptive Predator" had the Overwhelm property, so I mis-evaluated the resulting damage, which would have ended the game in my favour. The score should have been at least 5-3 (maybe 5+ - 2).
The final loss was a bad play in general, with I underestimating my opponent. One stunning spell and game over.