While playing random PvP1 I played against a fate egg deck. From one of the eggs, a Crusader hatched. Next turn (no weapons in play) I see that a NaN appears like the momentum symbol does and the Crusader's ability changes to undefined, and the 3
lost. The other player didn't know anything about it.
I then went on to test it. Jenkar helped me with 2 test-duels. First game, I tried clicking randomly first but (I think) it didn't work. Then I clicked randomly again but afterwards I clicked on the Menu button on the top left, then cancelled the popup box and endowed his flying vampire dagger. Another undefined crusader was made without endowing his weapon.
What I saw:
And what Jenkar saw:
I then asked him for another game. This game, I changed to a PU-crusader deck (to see if it works with PU) and I endowed the Menu with all my crusaders. Sadly, Jenkar didn't take a screenshot but he made his own undefined crusader after I told him how to. He also said that all my crusaders were shown undefined to him. The last, undefined one on my field on the screenshot below was a copy of his crusader.
So.. Mono weaponless crusader deck is actually possible! Useless but it is most certainly possible. Their passive skill changes to undefined too. 'Endowing the menu' does not prevent you from endowing other weapons, it seems to be a display bug only that is shown only to your opponent.
I suppose this works the same with the Send message box.