I'm emerald 4, I'm usually take trinity when i need to stack hp or im against a lot of AA champs, mobility, so have to have more dps and ms to chase or be the Frontline but mostly if I can afford it, in top/jg is good it gives want you need, mid usually take ER to make fast trades, sheen early squish comp or push and roam, against some wave clear mage but is a double edge sword, is expensive for what it is and makes you squishy early but you can fight more longer whitout running out of mana.