There is all the information in this thread, but it is very long, and finding it is not straightforward. @Barrelfish did a great job of summarising important rulings in the first couple of posts, but it’s difficult to determine what should go in them.
Basically, the reason the game works like this comes down to the interaction between 3 different kinds of effects: constant effects, triggered effects and state based effects. Units, building cards, heroes and upgrades have text on them, which either gives them abilities (such as Flying, or Resist) or effects, which can further be divided into constant effects and triggered effects. Triggered effects resolve using a queue system, which resolves the effects in the order they entered the queue. Constant effects apply from the moment the card causing them enters play until it leaves play, and ignore the queue system.
Finally, there are state-based effects. These are effects (which all come from the rules of the game, not cards) which the game immediately resolves as soon as they are relevant, and they are checked after anything happens in game. They also ignore the queue system.
So in the case of a player with a maxband Quince and a Mirror token playing an Abomination, the game state proceeds as follows:
Player plays Abomination, putting it on the table from their hand, and paying its cost in gold.
Abomination arrives in play, and triggers any arrival triggers. Quince maxband ability qualifies, and so ‘Turn a Mirror into an Abomination’ joins the queue. Abomination is now in play and so its constant effect is in operation
The game checks for any state-based effects - it finds that Mirror token has 0 hit points, and so Mirror token is sent to discard.
The game checks for state-based effects again - it finds a token in the discard, and trashes it.
No more state-based effects exist, so the queue starts resolving. Quince’s maxband looks for a Mirror to turn into an Abomination, but can’t find one, so the effect fizzles.