Many coliseum guides I've seen around here hinge on the use of the eliminate battle stone, which gives your dragon the power of a high-damage strength attack and refunds all breath if you take out the enemy.
This method is highly effective - your dragons are strong and fast enough to take out enemies before taking damage themselves - but it's also highly expensive and slow if you don't already have these stones at your disposal. Eliminate stones are a rare drop, so they're very time consuming to attempt to farm for. They are also expensive to purchase at the auction house.
The following is a somewhat less effective, but much cheaper way to farm a level if you're short on treasure or battle stones.
Choose your team
This build will help you to continuously defeat multiple waves of monsters without having to return to the main menu. This mechanic relies on the Aid ability stone, which restores a dragon's health after they have been hit.
It is very cheap to buy in the auction house and requires a dragon with high intelligence in order to utilize it effectively.
Your team of three will consist of two glass cannons and one mage/healer. For those who are unfamiliar with these terms, a glass cannon is a dragon that is high in strength and quickness, but low in everything else. This allows them to strike quickly and effectively before they get hit. The strength stat increases the damage they can do with one hit, and the quickness stat prevents them from getting taken out quickly by the monsters. A mage/healer dragon is similar, but with high intelligence and quickness.
Here's an example of this team from my own lair:



As you can see, the imperial has a high number of points in intelligence and the two spirals have high points in strength. Both have a high number of points in quickness as well.
Because mages utilize Meditate
rather than Scratch
they are slower to deal damage to the monster than the glass cannon. However, this one dragon will have the dual purpose of dealing damage to the monster and restoring his or her own health as well as the health of the other two. This will allow your team to stay in the arena longer.
Pick two level 1 dragons to be your glass cannons. They can be of the same element, or not. Each coliseum venue favors some elements more than others, so keep this in mind while choosing your dragons. To create a well-balanced team, you want to have a pair of contrasting elements.
A monster in the coliseum is aligned with one of the eleven flights, and some of them are neutral. Each element does increased damage to three other elements, and reduced damage to three different elements. You always inflict reduced damage upon a monster of the same element and they always do reduced damage to your dragon. When selecting dragons to pair with your first one, you want to choose an element they would be strong or weak against. Using one of these elemental combinations on your team allows you to be well-balanced:
Earth: Pair with Fire, Arcane, Lightning, Water, Nature, or Wind
Fire: Pair with Nature, Plague, Ice, Water, Shadow, or Earth
Wind: Pair with Earth, Lightning, Arcane, Shadow, Light, or Water
Water: Pair with Wind, Earth, Fire, Lightning, Plague, or Ice
Shadow: Pair with Ice, Wind Fire, Arcane, Light, or Plague
Ice: Pair with Water, Nature, Plague, Lightning, Fire, or Shadow
Lightning: Pair with Light, Water, Ice, Earth, Wind or Arcane
Light: Pair with Plague, Wind, Shadow, Arcane, Nature or Lightning
Nature: Pair with Arcane, Earth, Light, Plague, Ice or Fire
Plague: Pair with Shadow, Water, Nature, Ice, Fire, or Light
Arcane: Pair with Lightning, Shadow, Light, Earth, Wind, or Nature.
Refer to the chart here for more information on battle stones and elemental matchups:
http://www1.flightrising.com/forums/gde/1344211
Leveling up your team:
A dragon already comes with two battle stones, based on their breed. The two glass cannons will need Scratch and Shred, and the mage/healer will need Meditate and Contuse. If your dragons don't have the correct stones, you can buy these cheap in the auction house and change this under the Stats and Abilities tab.
Go to the Training Fields venue in the Coliseum and battle. Once you level up, follow the basic glass cannon build for the two dragons with Scratch and Shred. As a rule, you want to add two STR for one QCK point and focus only on those two. Do the same for the mage, but add two INT for one QCK point - this increases the effectiveness of your healing and magical attacks.
You may also want to add a few AGI points for either build, if you wish. Agility points will increase your chances of dodging an attack and landing a critical strike on the monster.
It's a good idea to stay in the Training Fields until your dragons reach level 5 - there's a big jump in difficulty between the first three venues. Once you reach the Woodland Path venue, you will want to stay there until you are up to level 8 before moving on to the Scorched Forest.
See this guide for in-depth instructions on leveling up glass cannons: http://www1.flightrising.com/forums/gde/1040710
Battle Stones
You'll need some battle stones to help your dragons - luckily most of the required ones have the chance to drop from the coliseum and are very cheap to buy on the auction house.
Your two glass cannons need Scratch and Shred, if they don't have these already.
Likewise, the mage/healer dragon requires Meditate and Contuse.
The two glass cannons each need one Slash and two Might Fragments of their corresponding elements. Make sure to not give them a Bolt as this build of dragon will do very weak damage with this attack. These can be added at level 5.
Your one mage dragon will require one Aid, which can be added after reaching level 3.
S/he will need one Bolt and two Acuity Fragments of his/her corresponding element. Make sure not to give him/her a Slash as this build of dragon will do very weak damage with this attack. These can be added at level 5.
You'll want to have these stones available once you level your dragons up to 9:
Fortunately, these three stones are not that hard to obtain, and you can frequently get any of them from Pinkerton.
The first item, Ambush, is an accessory stone. It can be added upon reaching level 9. You can add a second Ambush at level 15. The other two, Berserker and Scholar, are augment stones that can be added at level 17.
Once you reach level 17, you can replace your Might or Acuity Fragments with these better augment stones.
An additional option is the elemental ability stones that unlock on level 12. Like bolts and slashes, these stones can only be used by dragons of their respective element. They require the same amount of breath (20), and are frequently used by the monsters once you reach The Waterway venue (Level 16).
That's it, enjoy farming through the venues! If you are getting started with the coliseum or are looking for a less expensive team build, I hope this guide was helpful.



