Umbra armor has no effect if the enchanted creature is put into a graveyard for any other reason, such as if it's sacrificed, if the "legend rule" applies to it, or if its toughness is 0 or less
But, while Giratina ex and Darkrai ex are everywhere in the Pokemon TCG Pocket meta, they might not be as good as you think, with four decks currently having a higher win rate
It isn't like slam first pick or a core card I lock in my list right away but it does seem to be added eventually
The good news is that Unstable isnt like that
Counter Energy is very common in Mew FCO 29 decks which its ability of copying basic Pokmon's attacks, one of them being a "Single Prize" card, it could copy GX or EX Pokmon, and the most common are Garchomp & Giratina-GX UNM 146, Togepi & Cleffa & Igglybuff-GX CEC 143, Marshadow-GX BUS 80 and Amazing Rare cards, specially those who demand a lot of energy, being the most common one the Kyogre SHF 21
Approach of the Second Sun Not many cards say you win the game outright, though Approach of the Second Sun is one of them