Um. Wow. +5/+10, lifelink, blocks their whole attack. Wow.

Uh. Yeah, that's a bit too good for 5 mana, I suspect.

It is worth noting that it gives defender, so this is a purely defensive card. It requires a creature to do anything, however I do admit that unless it is removed or your opponent has a lot of power on board, it pretty much shuts down attacking for them. I increased the mana cost by 1, but I might need to do something else instead to balance it. Perhaps make it become unattached at the end of combat each turn?

That helps, but not hugely. Honestly; I'd be happier to see this as an instant than equipment.