While Cave Goblins commons define their play, they really need to summon their champions for the magic use and health they provide and Blarf is the maximum expression of that fact.
Always summon Blarf, it provides key life for the Cave Goblins while also providing a great way to dump your magic. It also synergizes extremely well with your events and Sneeks. There is no reason for Blarf to ever not join the horde.
Attack with Sneeks, Sly away for a 5-boost Blarf that you then attack with and then Enrage The Horde. That is of course the dream that you may enjoy some day with this card.