I dont know if this is just me but combining 3 expert mode drops from 3 fairly difficult bosses only to get a minecart is severely underwhelming, going off of the mechanical
Mechanical gear piece - Official Terraria Mods Wiki
Mechdusa - Terraria Wiki
Skeletron Prime - Terraria Wiki
Bone Helm - Official Terraria Wiki
Mechanical gear piece - Official Terraria Mods Wiki
Best Terraria 1.3 Items - The Mechanical Cart - Fastest Terraria Minecart [ Terraria 1.3] - YouTube
Steam Community :: Guide :: How To Summon And Defeat Mechdusa