My post on separating races and classes in B/X and BECMI lacked elves. Here they are:
- Maximum level: 10
- Experience modifier: +2000 XP for first level, keep proportions afterwards (so an elf thief-mage would level at 3200, 6400, etc).
- Hit dice: reduce 1 step (d8->d6->d4, where it stops, go to d3 hit dice if you really hate elvish thieves or mages)
- Infravision: 60 feet
- +2 to saving throws
- can cast spells like a mage of the same level, gaining access to them the same way (starting with a book). Spellcasting is allowed in armours or using shields if the class chosen allows to use them.
- Detect hidden or secret doors rolling 1 or 2 on 1d6 (for D6 Thieving: +1 to find secret doors)
- Languages: Common, Elvish, Orc, Hobgoblin, Gnoll.
Obviously the first elf rolled by a player turns out being an elf magic-user: that means two spellbooks, two spells at first level (one for being a MU, another for being an elf) plus an additional spell due to our high intelligence house rule.