Beast Riders really lead the charge. They are actually not the best at any role in the Cave Goblins and not being 0 cost units make them not the most synergistic with the deck.
However they are all-rounders, high reach, high damage, decent life, and are the main way of Cave Goblins to make use of magic, and because of that you should try to summon at least 3 of them every game.
They make your gates scary, even those that are far from the action, and they provide quick support to the army with a big come-into-play effect.
They also like to bring Clingers with them.