For example, if the equipped creature "has flying as long as it's attacking," it will not gain flying, even if it attacks after Colossus Hammer becomes attached to it
If a permanent card in a graveyard has in its mana cost, X is 0 for the purpose of determining its mana value
It also brings in the shiny reverse holo style and introduces cards like Dialga G LV.X
One thing we've seen over the past year of Standard is that the combination of cheap removal and heavily played planeswalkers that incidentally answer creatures (basically every Teferi, Oko, Thief of Crowns, etc.) makes it difficult to build around cards like Captain Sisay
The obvious use case is in Lathril, Blade of Elves, as youll be able to attack, get your elf tokens, and then be able to hold up her tap ability from the beginning of the next combat