More than once in my history of playing magic the gathering I have made the attempt to create a poison deck. As one of the few alternate win conditions I like the idea of poison but there were never enough good creatures and those that did exist were often weak enough that they could easily be blocked by the opponent's creatures. So in the end poison largely fell out of the game of magic, but many things that had disappeared return in time spiral and in the new age of magic when wizard better understands the game it was able to go just a bit farther with poison.
Snake Cult initiation is an uncommon enchantmen aura from the future sight expansion set of magic the gathering. It costs one black and three colorless mana to put into play and is one of the few enchantments that I have used in constructed or limited play.
What this gives that creature is the ability poison 3. This reads "Enchanted creature has poisonous 3. (Whenever it deals combat damage to a player, that player gets three poison counters. A player with ten or more poison counters loses the game.)"
Unlike most enchantment cards there is considerable value in this being an enchantment. The largest value is that it allows any creature in the game of magic to become a poison creature. This is something that is valuable because it opens up the possibilities so much farther than simply having another poison creature would have.
The first and most basic thing to do is put this on a creature with evasion. Even flying can allow you to hit your opponent with this, and since you need to give him only 10 poison counters to win it is as if you are doing 6 damage to him each time you hit him with that creature.
The second possibility is to put this onto a creature that already has poison. This adds 3 more counters allowing for a creature that could kill the opponent by attack three times or possibly even twice.
Sadly the truth is that poison, even with this and other cards in the time spiral block still isn't a truly viable tournament strategy. Creatures that use it are still generally to weak to easily make it through to your opponent and it is almost always easier to simply do damage, but poison counters are fun because your opponent will never see it coming.