There is a bug or an inconsistency with spell cost adjustments. Swiftscale Trickster normally sets mana cost of a spell to 0, which if played after an enemy Loatheb overrides Loatheb’s effect. However, I played Trickster after my opponent played two Cult Neophytes, and the Neophytes resolved after Trickster’s effect. Dragoncaster, Cabal Lackey, and Kirin Tor Mage all override Spell taxing effects, so why is this different?
I wrote a ticket but a blizzard employee suggested putting it as a discussion topic.
They have nearly the same phrasing:
Loatheb: Enemy spells cost (5) more next turn
Neophyte: Your opponent’s spells cost (1) more next turn
Swiftscale Trickster: Your next spell this turn costs (0).
Dragoncaster: If you’re holding a Dragon, your next spell this turn costs (0).
Kirin Tor Mage: The next Secret you play this turn costs (0).
Kabal Lackey: The next Secret you play this turn costs (0).
Here is a screenshot of the interaction: