The last ability is worded as both a trigger and a replacement effect. I would keep it as a trigger to allow for some interactivity from the opponents, which would then mean the "instead of your graveyard" isn't needed.
I like the effects overall and they tie very well together. 4 mana seems a little low but I am not always the best judge of the effects like this.
Enchantment
Whenever a creature you control deals combat damage to a player, you may discard a card. If you do, draw a card.
If you would discard a land, you may put it onto the battlefield tapped instead of into your graveyard.
As they pushed forward, the battlements moved with them.
Kind of like a Coastal Piracy / Toski, Bearer of Secrets effect. Should it be 5cmc?
I like the effects overall and they tie very well together. 4 mana seems a little low but I am not always the best judge of the effects like this.