Frogs are fast, even if you are encumbered, so are handy for traveling over areas you have cleared to visit traders, etc.
Your alignments change with your form. The spider statuette can be used to explore orc territory in peace (handy for the two army quests), or chase merchants out of their shops and loot (doesn't help with Kistandalius in Ars Magicana).
I don't know if the cat or bee/beetle statuettes have any particular uses. The beetle form may be able to attack shopkeepers or soldiers, similar to the alignment change with the spider.
Super drugs give +100 Poison resistance and -100 Spiritual resistance; the effect is temporary, though lasts a couple hours real time. They can be created using Alchemy from Drudanae herbs (the stuff George wanted you to get from Lanilor's garden at the start of the game).
Purple potions heal +20 hit points. It is better to sell then and use health or restoration potions.
Alchemy GuideBTW, if you delete both posts in your other topic (when you edit a post, there is a 'delete this post' button beside the 'change this post' button), the topic itself will be removed, as long as nobody else replies.