Large Crocodile

[Hypersmurf]

Can you not use it to offset the penalty to your effective level for having a bigger critter?

I would say yes, certainly - though there is debate on the matter.

However, that's not the problem.

A 7th level Druid has an effective druid level of 7. If he takes a Giant Crocodile companion, his effective druid level for purposes of calculating its special abilities is 1: 7 - 6. So Natural Bond can increase that - his effective druid level for purposes of calculating its special abilities will be 7 - 6 + 3 = 4, less than his hit dice... no problem.

However, a 4th level druid has an effective druid level of 4. To take a Giant Crocodile companion, he needs an effective druid level of 7. Natural Bond can't increase his effective druid level to 7, because that's higher than his hit dice. (He can take a normal Crocodile, and Natural Bond will make it tougher than a Crocodile companion to a 4th level druid without Natural Bond, but he can't take a Giant Crocodile.)

Druid level comes into play in two places - one for determining which animals you can take, and the other for determining its special abilities. The penalty only applies to the second, so for the single-class druid, its only the second with which Natural Bond can help.

-Hyp.