-decorative pets are just cute lttle things following your char that you equip in your wardrobe like a costume.
-looter pets are things buyable in the cash shop that collect your loot for your everytime a mob drops something
so here if you buy this collector you can decide to have the otter next to you or not and decide if the looter version otter collects the loot for you (a spell for that will appear in your spellbook)