You don't add or remove loyalty counters from Garruk Relentless when he transforms into Garruk, the Veil-Cursed. In most cases, he'll have one or two loyalty counters on him.

The second ability of Garruk, the Veil-Cursed doesn't target a creature. However, when that ability resolves, you must sacrifice a creature if you control one.

Garruk Relentless's first ability is a state-triggered ability. It triggers once Garruk has two or fewer loyalty counters on him and it can't retrigger while that ability is on the stack.

You can't activate a loyalty ability of Garruk Relentless and later that turn after he transforms activate a loyalty ability of Garruk, the Veil-Cursed.

The number of creature cards in your graveyard is counted when the third ability of Garruk, the Veil-Cursed resolves. Once the ability resolves, the bonus doesn't change if that number changes later in the turn.

Only creatures you control when the third ability of Garruk, the Veil-Cursed resolves will receive the bonus. Creatures that enter or that you gain control of later in the turn won't be affected.