Interesting responses on the animal companion thing.
I suppose there's nothing in the RAW about how a druid should treat an animal companion, so I can see an argument for trading out companions at will.
But I wonder how many druid players would role play it that way.
I said I had contemplated doing an AC swap when our campaign moved from a temperate forest area into a more desolate mountainous area, and I knew from the description of the campaign we were in that it was going to be a long quest. In the end I decided that the "special bond" between my druid and my animal companion was such that neither of them wanted to separate.
I base this on the role playing decision that an animal companion is not a tool that the druid uses, but is an actual "companion" that shares an emotional attachment with the druid, sort of like a person and a beloved pet, but magnified beyond even that bond, and so I attempt to play my druid as if she truly has such a bond with her animal companion.
But that's a role playing thing, not a mechanics thing. I can see how a druid could be role played differently and could be more of a "spread the wealth" sort of druid who believes that bonding with multiple companions over time is an important part of being a druid.
In fact that's making me think a bit about my own role playing approach. My druid is currently without a companion, having lost her third companion in battle recently and deciding as penance to not take a new companion for a while. Perhaps her reaction to this will be to approach the animal companion experience differently and decide that she should experience a wide range of companions WITHOUT killing them off.
Food for thought.