Transforming and Rolling Out
This Druid is pretending to be a Decepticon with Aberrant Wildshape.
In this section, we will discuss what happens when you manage to turn into a monster, via something like Wild Shape or Polymorph. We may also discuss a few side topics.
The rules for the various sorts of shapeshifting magic are varied and complex, and would make a whole handbook by themselves. A nice chart of the most common options is here. In this guide, we will focus on a few common mistakes. First though, let's make sure we're all on the same page:
Wild Shape, Polymorph, and Alter Self have gotten a lot of errata. Shapeshifting abilities are some of the most powerful and confusing abilities in the game, so the people who make D&D have put in a lot of effort to limit their power and make them less confusing. If you are going to use a shapeshifting power you need to make sure you have the latest errata, or that you have access to a trustworthy online resource like d20srd.org.
In general, a shapeshifting ability will tell you precisely what you do and do not get from it. If it doesn't say you get something, assume you don't get it. In particular, a shapeshifting ability will never give you the hit dice of the creature you are turning into, so you will never gain the features of its Racial Hit Dice, including its Base Attack Bonus, Base Save Bonuses, etc. You don't gain its feats or skill points either.
Many shapeshifting abilities are based on other abilities. Because of this, usually you can only know what an ability does by seeing what all the abilities it is based on do. For example, Wild Shape says that it functions as Alternate Form, except as noted in its description. Alternate Form then has a specific list of changes it makes. Because it's based on Alternate Form, we know that Wild Shape doesn't change the Druid's Creature Type, so an Elf Druid in the form of a Brown Bear is still an Elf. We also know that a creature that uses Alternate Form keeps its old Hit Points even if its Constitution score changes, so the same is true for a Druid in Wild Shape. (Because of this, Con is the second-most important score for a Druid, after Wis).
When a shapeshifting ability gives you the natural weapons of a form, it gives you the weapons, not the Attacks. This means your new weapons have the same damage, damage types (bludgeoning, piercing, slashing), and primary or secondary status as the creature's natural weapons, but do not have the same attack bonuses. Since you don't generally gain a monster's feats, you need to pay attention to whether its natural weapon damage is higher than normal due to the Improved Natural Attack feat.
Shapeshifting abilities often separate Special Qualities and Special Attacks. Pay attention to which section of the creature's description the ability is listed in, as well as to whether it is Extraordinary, Spell-like, or Supernatural.
Shapeshifting abilities do not automatically destroy gear. Instead, abilities will specify whether the gear falls off, resizes, or is merged into the new form. In a similar vein, most size-changing magic does not break enclosed spaces, instead the enclosure limits the creature's growth.
Usually, Shapeshifting abilities only let you turn into something average for its kind, which means that none of the modifications in the last section can apply to the creature you are shapeshifting into.
We will now discuss a few side topics.
Level-Drain Shenanigans: As was mentioned before, it's often kind of annoying to go running around with a lot of Racial Hit Dice. While some are very nice, others are quite weak, and none of them give class features like real classes do. If only there was some way to reduce your ECL by getting rid of them...
There is a very cheesy trick that can be done. If you have Racial Hit Dice and you lose a level (for example, due to failing your saves against a Wight's Energy Drain attack), you lose one of your Racial Hit Dice. The Restoration Spell says that it restores on Experience Level to a creature that has had a level drained. It does not say that the Experience must purchase a level in the same class that was lost. Because of this, some people interpret this ability to allow characters with Racial Hit Dice to lose their Racial Hit Dice and gain class levels in return. Since a monster's Level Adjustment is partially based on how powerful a character of their Hit Dice is, this can lead to very powerful creatures being accessible at lower levels. More to the point, this technique is based on a certain amount of hair-splitting silliness. Use at your own risk.
By learning about monsters, you have taken your first step to understanding the big sophisticated simulation engine that lies under what at first appears to be just rules to play a game. I hope you will continue to explore in this vein. The D&D 3.5 system may not be the best-designed or most realistic gaming system, but it is in my view one of the most intricate and beautiful.
I hope that you have learned the key lessons of this handbook. Repeat after me:
Monsters are just like me, except when they're not, and I'm a monster too!
Mommy, Daddy, guess what? I'm a monster!