Acorn
Silver-bordered cards are not tournament-legal and are not covered by the comprehensive rules.
Printings
Usually silver-bordered cards are printed in Un-sets (Unglued, Unhinged, and Unstable). However certain promos like the Holiday cards and the HASCON promos also use a silver border.
Mechanics
They feature mechanics that would be impossible to print in a normal expansion.[1]
Rules
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