Had the same thing with platform builder, until I remembered one tiny detail: you have to right-click with it first. The problem is - platform builder doesn't have ANY material set as default, so it doesn't know what to build with. If you press RMB while holding it - it will open up a menu with a few options you can pick.Alright, but seriously, the arena builder and platform builder items don't seem to do anything at all. I'm not too bummed out about it because it's just a slight time-saver. If those combinable potions didn't work, I'd be REALLY frazzled. It's pretty much why I love this mod so much. That explorer buff item alone is worth 50 platinum to me. What I wouldn't give to have something like that in other mods. I love freeing up my helmet slot for actual armor to get a set bonus on it. No more Miner's helmet for me, or carrying around a Shine potion.