Yes. MaD2 web and download use the same save format, so you can just move content around as you wish. If you save content locally, you can migrate it all over by moving the files (see FAQ > Local Storage), or you can manually copy save strings to move them.
There's no inherent limit on the game's end. You may be hitting Flash Player's size cap (though it should be asking you to allocate more space), or some kind of browser restriction.
I have 2 item suggestions because I suck at making things.
An item that can be added would be a Die. It starts with one black dot on it, but when thrown/is flung, rolls a 1-6 on random chance (you know, like a real die).
I think that a Thermobaric Rocket Launcher should be added, just because every other rocket (well besides the normal one) has an RPG Launcher for it.
That's it.
I found out a way to (kind of) make the automatically wearable armor. I just welded a custom helmet to a 'Praetorian Helmet', meaning that making a shoulder pad and welding it to a tactical shoulder (or any other shoulder armor) to your custom item should have it be similar to AW armor. It's can be a bit buggy, because the armor is not ghosted to alive things.
Can you add a property in the Resistances tab (Details) named "Resist Spread". The property should affect the object with it and have Transferring + Spread not configure the properties.
There is a glitch where hands are backwards after saving them as custom items as two different saves (such as V2s, and V3s). I've found a way to counter it, but I think that people shouldn't have to do something confusing in order for their custom items to work right. If there were any reports, I think this glitch should be solved.
Is it possible to add a property that makes items only make contact with Walls and items with Static/Weight 0? [Details > Properties > Physics > Item Ghost/New Property]
Is it possible to add the property of 'Static Ghost' on the Physics Tab? As said in the name, the item with 'Static Ghost' will not collide with any item with 'Static' on the Basic Tab.
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Yes. MaD2 web and download use the same save format, so you can just move content around as you wish. If you save content locally, you can migrate it all over by moving the files (see FAQ > Local Storage), or you can manually copy save strings to move them.