Ok, this is kinda hard-to-follow, but you play a {Lifelink} and a {Darksteel Plate} on {Boros Reckoner}, then you deal the {Reckoner} damage. That will trigger its first ability, so you have it deal the damage to itself. That causes you to gain 3 life from {Lifelink}, but since it dealt itself damage, it's ability triggers AGAIN, so if you do it enough times, you gain infinity life!!!!!!!!! :):):)
Tell me if you don't follow my instructions.
This is possible in standard
A well known combo with different components. Nice.
What's really cool is, once you move out of standard you can use cards like {Anthem of Rakdos} to spool up the amount if damage and then deal it straight to the opponent's face :)
Also see
{Furnace of Rath}
{Gratuitous Violence}
{Overblaze}