Help with Atomie as a PC

So we are starting a game at level 2 and a few people wanted to use ECL 1 and a class level. I said this was ok because most were all using ones that had them prebuilt. I have a guy who wants to use the Atomie. Since its a CR 1 does it mean its a ECL 1? If it does how would his stats look? It looks like a crazy broken ECL 1 if you get all of the spell like abilities, DR, Fly speed, and a sick stat line? If anyone has some advice let me know. Thanks!

Yes, you may need to redesign your game but in general based on player choice, and make sure to review their gear, the size rules, immunities, and ban certain choices. Right off the bat a diminutive creature faces alot of complications in that it must occupy the square of its opponent to attack. Wind will also be a factor for its size.

CR!=ECL. That creature seems pretty powerful. I'd recommend making it via the rules under advanced race guide (http://www.d20pfsrd.com/gamemastering/other-rules/creating-new-races)

Since a 2nd level player character is CR 1, I would probably go with playing the Atomie as listed in the Bestiary as a 2nd level character and then letting him gain normal class levels afterwards. Note that a Drow Noble has CR = character level, and the Drow Noble is a seriously overpowered race.

Yeah I keep looking at it and I don't want the headache and I'm going to take back the ECL race option. Everyone is cool with it except the Atomie guy...

Of course he's not cool with it! he wants to break your game. Just remember Diminuative creatures are imminently susceptible to grappling, and even a human could swallow one whole. Maybe you have a villain who believes the key to immortality is eating Fey. I often find that the best way to prevent players from breaking my game is to find ways to inflict the consequences of their choices upon them. I will generally allow anyone to play anything, but if its disruptive, I usually find creative ways to deal with those disruptions in a way that does not seem as though I am picking on the PC unduly. Of course it helps that my players know that every encounter i run is potentially lethal and without intelligent play they could easily die.

Yeah - having critter like that being played would be a very bad idea.

Frankly - I'd never allow anyone to play a race that wasn't small or medium, and with dervish dance or now slashing grace, he wouldn't even take a penalty from the reduced strength.

Actually - I might let him play it, but I'd rule that it's a LA +6 race or something ridiculous, while getting a huge advantage from the dex.

Back in 3.5, a lot of the LA races were basically priced out of range like that. You want to be a vampire? Sure! Just be 8 levels behind the rest of the group! (obviously unplayable)

even with the Dex, his CMD is going to suck. grapple disarm and sunder will ruin his day.

So we are starting a game at level 2 and a few people wanted to use ECL 1 and a class level. I said this was ok because most were all using ones that had them prebuilt. I have a guy who wants to use the Atomie. Since its a CR 1 does it mean its a ECL 1? If it does how would his stats look? It looks like a crazy broken ECL 1 if you get all of the spell like abilities, DR, Fly speed, and a sick stat line? If anyone has some advice let me know. Thanks!

First I always wanted to play an atomie too, therefore I might be biased. Those little guys are pretty awesome.

Yes ECL=CR. Therefore Atomie [Insert Class] 1 woould count as level 2 character. However those guidelines for monsters as Characters are just fast guidelines and specifically call out for you to adjust. Often they can be really broken otherwise(Pseudodragon Sorcerer).
I'd probably count the Atomie as ECL 2 at the beginning(2racial HD, some pretty useful Spell-Likes, nice stat boni, fly speed, +d6 SA). At higher levels I'd reduce the level adjustment to +1, since Fly becomes more acessible and his Spell-Likes will fall off too.
You should also consider, what class he wants to advance in later. As a caster the extra defenses from the small size and statboni might not be worth losing two levels of spell progression, therefore an ECL of 1 would be ok from the bat I guess.
As a Dex-based martial/rogue/bard on the other hand the exchange would easily merit an ECL of 2.

If you use the Race builder do it together with your player and discuss, what he likes about the Atomie. Maybe he is ok with dropping the Racial HD and Spell-Likes because he wants to be a just super small fencer.

Seems like an ECL 2 period.

The creature has fantastic strength for a Diminutive creature (Paizo puts base strength at that size at 1 for monster generation).

Base stats for a Diminutive creature would be like: 1/16/8/11/11/11. With the odd/even of any stat not mattering so long as it doesn't drop a modifier point.

This gives the Atomie: +4 str, +4 con, +4 wisdom and +8 charisma. There are no stat penalties outside of size adjustments. Even if we assume this was made with the elite array, it's still balls strong.

Add permafly, useful SLA's, Proficiency with all simple weapons, 2hd, good saves, great skills and this seems easily like a ECL 2.

They no longer use ECL or LA. That was 3.5.

Pathfinder has rules for it as earlier mentioned in the Bestiary Monsters as Characters. SO by the rules an Atomie would fit in with a group of second level characters if he was level 1.

With that said if you are unconfortable with it simply tell him No. Some things are not up for debate and if the GM says NO then it is NO.

Just as if you wanted to run in Golarion and he demanded you run it in Forgotten realms becuase he preffered that setting.