I am at a loss at finding a proper ruling so it shouldn't hurt to ask the community ^^ a friend and I played a bit of magic and came to an impasse, he attacked with 4/2 with trample and I blocked issuing my cartel aristocrat after using the gain protection ability from a color of the attacker. Problem is does any damage go through? We think it does but it would be nice to have hard evidence to it you know?
Yes! Trample is the key here.
{Cartel Aristocrat} is a 2/2
Trample gives the creature the ability to assign any unassigned damage to the player, AFTER assigning enough to kill the creature.
Therefore, the 4/2 assigns the aristocrat 2 damage and is left with 2 to deal on to the player.
Both creatures would normally die, except the aristocrat is given prevention from the damage, and the damage is then reduced to 0.
{Cartel Aristocrat} survives, 4/2 creature dies.
For the rulings on trample see 702.18
For the rulings on protection see 702.15