Can someone summarize what cardboard elements or print and play is Modern Age legal?

Character cards. I think that is it, sadly.

Character cards, ATAs and cardboard special objects that are from Modern Age sets.

Oh yeah, ATAs. I don't think there are any 2D special objects in the modern age sets though.

thank you! Is that all ATAs or are they set dependent?

ATAs are not tied to any specific set, so they are not ruled by retirement/Modern Age restrictions.

Just ones that are part of a figure (Caps Shield, Scorpios Key)

There's also the BST from Squirel Girl, Falcon, Bruce Banner and Thanos

Can't think of anything else from WK site

None of them are really print and play though as they cannot be played independently...

Yet in the case of Bruce and the Thanos bystander, if you don't print them, you'd have nothing to play on the board (that traditionally reflects the piece anyway).

bump for clarification.
Are the special 3d objects legal in modern, but the vines that heal (i foget thier name) aren't because they're in a golden age set.

Special objects are legal in modern age if they come from modern age sets. Being 3D does not factor into this, so Mjolner is golden age because Hammer of Thor is. Currently, none of the "pog" special objects is legal, but that's only because none have been made in forever. I think the last ones were in Secret Invasion.

i was meaning more like the trash container that can be used twice, the soda machine, the desk, and my favourite the shipping crate you can throw 10 instead of 8.

Are these items legal?

Those are golden age items.