Some of the Vampire cards from Innistrad have abilities that grant them +1/+1 counters when they deal combat damage to a player. Stromkirk Patrol is an example of a vampire with this ability.

Rakish Heir has a similar ability, but with an important difference as it can make all of your other vampires even better. Its ability triggers whenever any vampire you control deals combat damage to a player, and that vampire will gain a +1/+1 counter. If you control a Rakish Heir, the Stromkirk Patrol mentioned above will end up gaining two +1/+1 counters when it deals damage to a player, one from its own ability and one from Rakish Heir’s ability.

Rakish Heir’s ability will also affect vampires you control that do not normally gain counters at all. A Vampire Interloper doesn’t have an ability that gives itself counters, but Rakish Heir’s ability will give it +1/+1 counters when the Interloper deals combat damage to a player.