So if you have just unlocked the coliseum or are about to I have great news for you. The coliseum is an easy way to rack up lots of free gems on a daily basis. Easy that is if you know a little about what you are doing, which hopefully this will help you do.
First thing you probably will want to take note of is the constellations. Constellations are changed on a weekly basis and provide bonuses to some heroes. There is a turf quest for using 5 heroes who receive the bonus; however, after you pass the quest, a hero receiving the constellation bonus is not necessarily your top consideration. It is good though to take note of the constellation change as you may want to change your defensive line up.
Next you should get your defensive line up set. This is the heroes that your opponents will face when they challenge you. There is no magic bullet but you should balance it out between tanks, damage dealers, healers, and support. Higher might is generally good, but you should not necessarily just go for the highest might possible. The rest of the guide will help you picking your line up.
While I will go into some recommendations about specific free and pay heroes, due to changes in the game meta and constellations, no advice is either fool proof or set in stone. A really good way to see what are the best heroes to be using both for defense and offense is in the top 100 list. If you check the rankings for individual players there is a tab for the coliseum, and you can see the line up for all of the top 100 players by clicking the might button. Another way is to check the heroes the people ranked near you are using. Ignore the guards as they are npcs not other players. If you click their leader icon it will show you what their line up is. This will give you a good idea of what the best heroes are to be using at the time. While you may not have all the heroes any that you do have you should try to level up, rank up, promote, and get equipment for.
In prioritizing these things I would say the first priority should be to get equipment, and rank up whenever possible. The second priority should be to level max. To a good degree this goes hand in hand since equipment has level requirements, and farming equipment will get you experience boosters to level up with. When farming I definitely recommend farming elite whenever possible; however, if you really want to stay as high in the rankings as possible you will sometimes need equipment that you do not have access to in elite and waiting can cost you a lot of gems sometimes. Rarity is going to be your lowest priority. Rarity effects battle skills more than base stats, and battle skills are not going to help you in the coliseum. This is really good news for anyone who is willing to spend some money because it means that you don't necessarily need to spend a lot to get some good value in the coliseum.
Before we get into hero recommendations let me give some advice on picking battles. You should be ranking up as quickly as possible, and this means using your daily battles to move up as many ranks as possible. When choosing opponents it should generally always be the opponent at the top; however, you can click the change opponent button to see all the different people available at the top, but if you are choosing the middle or bottom opponent you are not going up in rank as much. This is okay if you are at a threshold where a few ranks will make the difference between one level of gems and the next, or if it is close to reset time and you are not confident that you can win the battles so you want to do some experimenting. When you are just beyond a threshold you should save some battles for when you get knocked back down. Even the best defensive line ups will lose, and being able to recross the threshold will help you get as many gems as possible. Experimenting can be very useful and can give you an edge in the current meta where you realize that a hero is useful although not widely used, but it should be done close to reset (or as close as you will get) when you have extra battles left.
Okay finally we get to the hero recommendations. I am going to start with the free heroes. If you look at the top 100 in my kingdom currently you will see a lot of people using Tracker, Demon Slayer, and Rose Knight. You can get them in that order. These heroes seem to be pretty consistently valuable despite constellation changes and probably will hold up over time; however, nothing is no fool proof or set in stone. Tracker and Demon Slayer are good because they both do a lot of damage, and they both target the heroes at the back, which if you can kill quickly will generally net you a win. Up until you notice these guys are not being used frequently obtaining them should be your goal. Rose Knight is a decent tank, mild stunner, mild healer, and awesome shielder. She can be hard to get but I recommend using YouTube guides or whatever to get her as soon as possible. In many cases she will completely eliminate all damage taken for the first 8 seconds of the match. Prima Donna is also frequently used and for good reason; however, there are good pay substitutions for her. If you are strictly f2p then she will be a priority as well. People can actually make an argument for almost any of the other f2p heroes, and if you have one leveled, ranked, and it has a constellation star then its probably a good bet. Once again check the rankings to see what other people are using, and try to tie the heroes together in a way that makes sense like child of light with magic users. There is a lot of other guides that cover good hero combinations.
For pay heroes right off the bat I will recommend my personal favorites Lore Weaver, Berserker, and Dark Follower. Lore Weaver gets a ton of play currently and for good reason. She can often make a better healer than Prima and has other skills that generally make her more valuable than Prima. Berserker I don't see used as much but I think she is good. She is a decent tank with a better than average ultimate. Her freeze can easily net you several wins. Dark Follower makes as a good secondary healer and good support. Big Guy gets a lot of play, but my opinion it is because a lot of people have him, not because he is the best pay hero to use. If you do have him he can be a worthwhile tank, but I don't think I would recommend buying him specifically for coliseum, and you may find times where Oath Keeper, Child of Light, or Death Knight are flat out better choices. Again here you should be checking the rankings. I want to emphasize again that rarity is of minimal importance so don't feel that you shouldn't be using pay heroes because they are only common. I have gotten into the top 10 of my kingdom using both Weaver and Berserker at common. Due to the return in gems you can get by using these heroes I think the $5 can be a great deal. Also its a lot cheaper to rank them up in rarity if you are waiting for them to rotate in and out.
Well for now that's about all I have. I hope this can be useful to you lords and ladies. I look forward to reading your comments, and I will try to keep it updated with more useful information, but my best advice (as you can probably guess) is to check the rankings.
This is great! I wish I could have read this when I first started out. I think the colliseum is one of the most confusing parts of this game, and this post answer all the questions new players are bound to have.