The Bug Update introduced the 5th Troll in the game (Dazzle), making it much easier to find the full (4) Trolls bonus. This makes the Trolls + Dragons combination much more consistent than before.
Unlike the build above, this build needs levels more than upgrades. The reason is that you wnat to find a Troll Warlord sooner rather than later and ideally to upgrade him to two-stars. The only three-star you're looking for in the early-game is Luna, all the extra gold should go into experience.
Pushing for lvl10 is also possible because it will allow you to complete one additional Alliance - either (3) Healers/(2) Heartless with Necro, or (2) Dragons with Viper.
Last but not least, if you spend a lot of time on lvl9/10 you have a good chance of finding a two-star Sven. Even though Sven has a bad reputation for an Ace hero, replacing a weaker two-star Knight (e.g. CK) with a two-star Sven is almost always worth it. If you are afraid that your army will become too squishy, place Sven at the backlines to make sure he doesn't activate his ultimate too-early on when your opponents are using their crowd control.