This information is accurate as of March 13th, 2021. The game is frequently updated and things change, while this post most likely won’t get updates, so if you are ready this months later, double check to make sure the advice still applies.
I have been playing Mighty Party for a year now, having reached league 1 on my Steam account rather quickly (legacy rules where progress was super easy) and league 8 on my mobile account (normal rules). I have spent some money across the two accounts, but am certainly no whale. Below are the most important tips or advice that isn’t clear to new players. Note that this advice is from the perspective of wanting to advance as quickly and efficiently as possible. That’s where I find the fun in games like this. If that’s not your direct goal, play however you want to have fun; it’s a game after all.
About spending money: The most impactful thing you can buy in MP is a legendary pet, which costs $50. It’s a high cost but they can’t be earned in-game, and have a huge power impact. I think of buying the pet as upgrading from the trial version of MP to the ‘real game’. The best pet to buy is Drogun, primarily for the +hit point ability, which will let you establish board control and scale your heroes out of reach. His direct warlord damage ability and his +attack boosts are also nice of course. Sentry is the only other pet to consider, as his immediate +attack is very nice, but right now Drogun is just better long-term.
You want to buy the pet as soon as possible (unlocks at league 16), because the sooner you have it the sooner you can start doing the Hunts to level it up, and because the best time to Hunt is during High Growth fable, that will naturally limit how quickly your pet levels up each month.
After the pet, the gem fund from Journey mode for $20 is great value in terms of cost/gems. This expires after some time, so if you are going to spend some money on the game, after the pet don’t let that expire. Beyond those two items everything else is of lesser value, and what to buy and when is more situational. Another good use of money is chest slots, especially if you play on PC, as on that platform chests all open at the same time, so the more slots you have, the more chests you can open. If you plan to play only on mobile, chest slots have less value, though it is nice to have the extra space to store bigger chests to be opened during events.
With the recent removal of Raids, there are now only two game modes that rotate: pit and dark tower. Both of these scale in difficulty based on your total might, a hidden value that is the total power accumulation of your account. Doing well in these modes will earn you a significant amount of extra resources, so it is important to try and limit how much your total might grows. Because of this you want to avoid soulbinding any hero besides what you need for an event, and the current 8 heroes you use. Soulbinding anyone else will inflate your total might for little gain. You also want to avoid using reborn on most heroes too early, with my rule of thumb being level 16 for commons/rares/epics before I reborn. Legends are a bit different as you often need to reborn one for hunts, and when a reborn fable comes around its not a bad idea to take advantage of it. Once heroes are at 16, it’s good to start evolving that hero to its higher rarity rather than leveling it higher.
Making the most of the High Growth fable is also very important. While it may be tempting to level what you can each time, sometimes the correct choice is skipping a HG to go all-out the next one. The gold cap is 3 million, so getting close to that and then doing a HG is ideal, because the gems-per-level is higher after the first 5 tiers in HG. If you end up just short of levels, this is when using a reborn or two can also make sense.
The best use of gems is first to buy the pirate skin, its by far the most powerful warlord skin for anything outside of League 1. After you have the pirate, you want to save up gems to use in an event that has at least one top-tier hero. When that event comes around, you want to use gems to first reach chapter 3 on the first day, and then keep pushing as much as you can, including buying the warlord skin for that step in chapter 3. The more bosses you unlock early, the more times you can kill then after a refresh for sparks. Don’t waste gems on events with sub-par heroes, and never waste gems on things like summons or the wish shop.
Top tier heroes can change as balance is adjusted, but currently these are the heroes that will help you climb and are less level dependent: Shadow Shaa-moona, Dead Lord, Groot, Frost, Blair, Santa, Justia, Iceburg. This gives you plenty of direct removal, silence, and delay, while your backline is a ticking timebomb with Justia buffing attack. This is important because if you are progressing quickly, you will be facing accounts with heroes 2x+ the stats of yours, meaning you can’t rely on direct damage to kill them. Any hero that is only good when “its high level” won’t work for you, since you will always be under-leveled vs what you are facing.
The above covers some of the major points. There are countless smaller items and adjustments that will help or hinder your progress. Discord is the best place to ask those.