Ran into this yesterday. Invisible Stalker is in a zone with a creature with Guard. Stalker is Invisible and has Elusive and Pest.
Elusive lets you ignore creatures with Guard but as soon as the Stalker declares an attack it loses Elusive.
We eventually decided that since the Guard trigger and the loss of Elusive happened in the same step that I, as the controlling player, could determine what order they happened in.
I am just wondering if that was the correct solution?