Harz IV is a freebee add-on to the game Igels. It was distributed during the Spiel 2006 and was also included in the magazine Games Orbit, printed by Pegasus Games.
The card is a reference to the social/unemployment benefit "Hartz IV" granted in Germany. Also, it is a word-play as the German word "Harz" means "resin" and this is were the card comes into play. Here is the card's text:
"Wer einmal in die Harzfalle tappt, kommt kaum noch vom Fleck. Harz klebt sofort vier beliebige Gegner zusammen, die in dieser Runde nicht mehr weiter gespielt werden können."
This translates roughly into:
Whoever falls just once into the resin(Harz)-trap makes hardly any headway. Harz immediately sticks together any four enemies, who cannot be played any further this turn.
The two cards Harz IV cards you get are simply shuffled into your standard card deck. They are of the "Unterstützungskarten" (support cards) type and can be played as any support card can in the support phase of any combat.