The Chaos Elemental card can be obtained by crafting 70 Ruby Gems and 2 Ariane Legend Tokens. It is also available from booster packs.
Upon Beta release, this card's effect erroneously read as follows:
Both Legends lose all their cards and draw 5 new cards.
This was fixed on 15/12/15.
In RuneScape Edit
The Chaos Elemental is a boss monster that resides in the deep Wilderness. It is noted for having "chaotic" attacks, including the ability to disarm players and teleport them away.