I am testing something which allow me to spawn Giant on top of mountain in an Extreme_Hills Biome. It work great, the issue is about giving custom drop to Giant, maybe I do something wrong or there is a bug somewhere. I have see the Creature List of OtherDrops page and Bukkit Entity name and use Giant.

This is the code to spawn Giant. The tower is actually highest place around in the biome, so only Giant can spawn there

 CREATURE_HOSTILE:
  - action: MOBSPAWN
    drop: GIANT
    height: ">170"
    lightlevel: 4
    message.server: "&cA player&f found a &7&LGiant &f on top of the tower!"
    chance: 100%

#When I add this code, nothing work at all, it's like it does'nt recognize "GIANT" and screw the rest of the code:
GIANT:
- drop: EMERALD/25-50/35%
- command: "/*rpgitem gaxe give %p"
message: "&c%p&f found an &9&LAxe of the Sky Son &f!"
chance: 5%

I don't think that's because of the command, which is also use with other Mobs and work perfectly. Everything work on the Online Yaml Parser. Thanks for your support!

CREATURE_HOSTILE has 5 spaces in front and GIANT has 4. Don't know why YAML online didn't error on this but I did notice that if you copy and paste this that only the creature_hostile part appears on the right.

Thanks for pointing that, I hope it will help other people with that kind of issue. Everything work well, sorry to have bother you with that!