Colossus Hammer
Artifact — Equipment
Equipped creature gets +10/+10 and loses [[ keyword: "flying" ]].
Equip 
"Relic retrieval is delayed. Mentioning it was forty feet tall might have helped us prepare." —Queen's Bay Company dispatch
Julian Kok Joon Wen
Rulings
Colossus Hammer can be attached to a creature that didn't have flying to begin with. It just won't lose flying.
(wotc • 2019-07-12)
If an ability of the equipped creature states that it has flying "as long as" a particular condition is true, that condition becoming true will not cause that creature to gain flying. 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.
(wotc • 2019-07-12)
If the equipped creature gains flying after Colossus Hammer became attached to it, it will keep flying.
(wotc • 2019-07-12)
Rulings
Colossus Hammer can be attached to a creature that didn't have flying to begin with. It just won't lose flying.
(wotc • 2019-07-12)
If an ability of the equipped creature states that it has flying "as long as" a particular condition is true, that condition becoming true will not cause that creature to gain flying. 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.
(wotc • 2019-07-12)
If the equipped creature gains flying after Colossus Hammer became attached to it, it will keep flying.
(wotc • 2019-07-12)