OK, to get these guys going, let's figure out ability scores for them, as they are usually the key to unlocking the rest of the creature.
First, we know Int is 5. Cha should probably be 1, as a few other intelligent oozes still have Cha 1 (like the assassin jelly). Wis is probably average (10-11).
Str would appear to be 18-19 for the gold (based on +4 dmg), and since the other two deal +3 damage over that, probably 24-25 for the platinum and iron.
Dex could be high to achieve the AC of 15. The assassin jelly, for example, bucks the usual ooze trend of low Dex and no natural armor, going with +2 Dex, +3 natural.
Oozes generally have decent Con, many 20 or higher.