Two Worlds

This is easy to do when you fight any of the lower sentient creatures (Grom, Bandits, etc). Many of them will have similar gear, so just collect what you can carry, and combine until the achievement pops. I was able to do it with the Grom Shield and a couple different weapons.

If you are not familiar with the process to combine items -
Y (while on the item) to bring up the menu
X to select Combine
X again to select the item to combine with
Items that are eligible will turn green.

There is a necromancer tower a couple of miles above Windbreak Village; not surprisingly, there are a bunch of necromancers here, and they all use the same staff weapon.

Defeat the necromancers; to make the fight easier, use a potion or item (like the zombie glands) to better protect yourself against the necromancers' poison attacks.

After you've beaten the necromancers, gather up their staffs. To combine the items, go to your inventory and select one of the staffs; press Y and then X to combine the green-highlighted staffs. Do this for all the matching staffs in your inventory.

Even upgraded 10 times this staff is still pretty weak, so you probably won't want to keep it for very long.

After the orc attack on ashos, you can gather Katana's and Katana Gomai from dead guards. I found over 20 and combined all of them to earn this. The weapon is powerful, too.