This is a rather simple idea, allowing Fragger and Thunder to throw out body armor to their team mates, which will allow them to take 20 more damage before wearing off.
So Skyhammer gets 140 hp temporarily, then once he dips below 120 it disappears. A simple a way to give more of a role for them to fill.
Just throwing something out there, probably garbage.
Over in the Mercenary/Skin Suggestion section, we generally frown upon any ability suggestions that modify the HP/speed ratio in any way. Mercs with the armor (and the merc who hands them out themselves) have a straight up advantage in a 1v1 HP-wise, assuming both opponents have identical base HP values.
Also, if Thunder can give himself armor, that’s 180 HP he has. I also wouldn’t want to fight a Proxy with 110 HP who has the same normal speed. The only way armor could be balanced in DB is if a merc wearing it also took a temporary hit to their movement speed to maintain the HP/speed ratio.