Justimon focuses on changing your Justimon into different arms and stacking the digivolving effects for each tamer you control
When this card leaves the field: Destroy all monsters your opponent controls
But that downside isnt really a downside, as in the Abyss Rising format, you would just use the monsters for material for Xyz Monsters such as Madolche Queen Tiaramisu , Leviair the Sea Dragon , Wind-Up Zenmaines , or other Rank 3s and 4s
Basically if the original card is legal, the promo is also okay to be played in that format
Yuto's "Phantom" Spell Cards also have secondary effects that can be used when they are in the Graveyard, so if they are destroyed while they are on the field, Yuto can still utilize them
A "K9" Xyz Monster that has this card as material gains this effect