For Larry Franklin @boston892

Over on twitter Larry Franklin was looking for some help and I thought I'd oblige him.

@Thatakinsboy @DreadGazeebo yeah i do im trying to make an arrow demon a playable character keeps his bonuses but stats are rolled like any
— larry franklin (@boston892) August 12, 2014

@Thatakinsboy @DreadGazeebo other character i would also like to change his alignment as drizzt didnt go the route of the spider queen
— larry franklin (@boston892) August 12, 2014

Okay the the Arrow Demon (MM 3, pg. 34) has a level adjustment of 8 which means that you won't be able to level him until you reach 36,000 experience points, or 9th level. With such a high level adjustment most people don't play them unless they couple their advancement with the variant rules from the Savage Species book which allows you to progress along with the rest of the party and not to dominate everyone from the get go. To simplify things, though, we'll just assume that your DM has you making an 8th level character so that you don't have to worry with the long slog as your friends level over and over again and you remain the exact same the whole time.

To determine your ability scores for your monstrous PC you need to take each ability score and subtract 10 from even scores and 11 from odd scores (DMG pg. 172)

Your bonuses to your ability score rolls:

Strength: + 10

Dexterity: + 8

Constitution: + 17

Wisdom: +4

Intelligence: + 6

Charisma: + 2

Okay, your hit points are determined by your Hit Dice (DMG pg. 172) with the first one being maximized to represent your first level. An Arrow Demon is classified as an Outsider so you have d8 Hit Die (MM pg. 290)

Your Hit Points:

8 + Con Modifier + (9d8 + 9 x Con Modifier) 

You get +10 / +5 attack bonus. Your Fortitude, Reflex, and Will saves all have a + 7 bonus. You have 8 + Int Modifier for each of your 10 HD, and you have 5 feats to choose from (MM pg. 290). As for the alignment just ask your DM if you can ignore that requirement. If she's letting you play the Arrow Demon then she probably doesn't care about the alignment restriction. 

Oh! One more thing before I wrap up: ask your DM about how much starting treasure you should begin the game with because there may be restrictions on how much she wants you to have access to at the start of the game.