In Dungeon Boss there are two different levels. One is the Player Level. It is the limit that your Heroes can reach and raised by completing Daily Quests, succeed in Dungeon Raids, and beating Dungeons. The other level is the Hero Level which is raised for each Hero individually by beating Dungeons and consuming XP Potions.
See the main article Leveling to learn more about leveling up your Heroes.
Player Level Progression
The Player Level limits the Heroes' level, but also determines how much stamina and friend slots you will have. The XP requirement increases exponentially. The table below shows how much XP is required to reach the next level, as shown in-game.
The difficulty of Dungeon Raids and The Tower of Pwnage is set by the Player Level. It is recommended to keep the levels of your favourite Heroes as close as possible to the Player Level. A difference 3 levels is fine. The Challenge Mode update raised the maximum Player level from 61 to 70. The Update on May 25h, 2018 raised the maximum Player level once again to 80.
Number of Friends
The number of friend slots starts with 10 friends at level 5 and ends with 33 friends for level 70. For every 3 Player Levels you gain another slot: Number of Friends = 10 + (Player Level / 3).
VIP Level 2 and 6 grant +5 and +10 extra friend slots, respectively.
Hero Level and XP Progression
The XP requirement to level up a summon increases exponentially, but with a much higher increase than the Player Level. To level up a new summoned Hero from level 1 to level 40 it requires 18,595 XP. To level up that Hero to the maximum level of 60 it requires another 141,500 XP (=160,095 XP for level 60 minus 18,595 XP for level 40). So the final 20 levels cost about 7.5 times as much XP, additionally. The new maximum level 80 which was introduced on May 25th, 2018.
The table below shows how much XP in total is required to reach a specific Hero level, as shown in-game, and the increase for each level. If you divide the total XP by the size of XP Potions you will get an idea how many potions are needed.
The current maximum Hero Level is 80. The tier of an ability can't exceed the level of that Hero.
The gold needed to upgrade a Hero's ability increases exponentially, too. To upgrade an ability from tier 1 to tier 60 a large amount of gold (855,500 gold exactly) is necessary. Depending on the number of Ascensions Heroes can have up to 3 abilities. This can tripple the amount of gold needed to have the Hero at full power.
The table below shows how much gold in total is required to reach a specific tier (level of an ability) and how much gold is required to reach the next tier, as shown in-game.
At VIP Level 4 your Heroes will start at a higher level when summoned.
Progression in table form
The following table answers the question how much XP and gold is required to reach a specific level and tier or the next level and tier of an ability.