I may be a little biased because I'm a huge Tolkien fan, an Avatar nerd, and I love me an RPG, so Universes Beyond sets definitely excite me
A battle happens from the point you declare you wish to attack, and thus any effect that prevents cards from being activated at the point of a battle starts cannot be activated, see the first example below for how to write that kind of effect
In Tempest, it was turn one (Mogg Fanatics, shadow creatures, and flyers), Invasion turn two (2/2 bears for every possible color combination plus several one- and two-mana apprentices and utility creatures), and Mirage turn three
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If this card is sent from the hand or field to the Graveyard