Goblin Tunneler has an activated ability that makes a creature with power of two or less unblockable for the remainder of the current turn. This ability does have a targeting restriction which requires that the targeted creature have a power of two or less. In other words this creature’s power must be two or less in order to activate the ability, and if this creatures power is greater than two when the ability resolves the ability will become countered on resolution.

However, once this ability resolves the power of the creature that was targeted by this ability does not matter any longer. For example, if you were to target and resolve a Benalish Veteran with this ability, the Veteran will be unblockable for the rest of that turn. It does not matter that the VEteran will get +1/+1 from it’s own triggered ability when attacking, it will still be unblockable.