you can choose any amount, but beware the consequences

any amount; you control water, but are always thirsty; you control plants, but plants are growing in you painfully; you control fire, but are always burning; you control dreams, but always have nightmares; you control blood, but have a insatiable thirst for it; you control acid, but are not immune to said acid; you control light, but darkness hurts you; you control darkness, but light hurts you; you control ice, but are always freezing; you control metal, but at the expense of iron in your blood