Once you joust the guy on the bridge unlock the gate and ride into the field. Stay behind the Carriage killing the boar riders as they shoot the arrows onto the carriage,they cause it to catch on fire. When it catches on fire, make epona go faster, wait till the carriage is targetable and use your boomerang to put it out. When the birds come make sure your bow is on the directional arrows and once again make epona go faster, target the birds and drop them.
I did it first try, if the wagon is diverted due to the bombs just follow and repeat the steps to protect it.