The relic Montain's Heart has a -3 speed modifier. If I placed it on Ironwolf and placed Ironwolf on a mount to form a cavalry unit, does the cavalry unit get the -3 to speed?

I guess the question can be generalized to the other relics which reduce or increase speed as well. Would the increase/decrease of speed on a rider carry over to the cavalry unit?

What's the latest ruling on this? Thanks!

Nope! When you move a cavalry unit, you always use the mount's speed.

Thanks! I guess that would go for the front arc as well?

Ignore the rider's speed and front arc when he is mounted. He will always use the mount's speed and arcs.

Does the mount also get the +3 defense which the Mountain's Heart relic give or just the rider wielding it?

Just the rider does.

for a general rule of thumb, relics only modify the wielder unless stated otherwise on the relics.

-saber