What Keystone mastery do I take on Bard?

Windspeaker gives your allies more resistances and boosts your healing.

So you can give them more clutch defense in fights.

Otherwise you can still go bond of stone.

Does he shield people? No? Okay? Does he need a 5% boost in cdr? Stuns for days son. Maybe thunderlord... if not then you are sorta outta luck. But I think that would give his meeps an welcome added effect.

I'd say Windspeaker's Blessing or Strength of Ages.

Ima just leave this here :3

https://www.reddit.com/r/bardmains/comments/3y3dwr/ap_sup_bard_too_fun/

If no Keystone is really attractive, look at the tier 5 masteries and take the column you want the most. Then chose the less bad mastery in this column.

For an utility-based supp, I'd say you want the +5%CDR, and then both Thunderlord and Windspeaker are not too bad. You can proc TL relatively easily with meep-empowered aa, and the bonus flat resistances given by Windspeaker is good, even if the bonus on your heals isn't so useful.

If you finally decide to go 18 into resolve, Bond of Stone is not bad, because there is still the selfish damage %reduction, even if you don't care about the ally's protection. And Grasp may need a bit of practice before getting it right, but if you manage to proc it when you poke, it's also interesting (but not ideal if you don't build tank, because 3% of your max HP is not a lot).