Getting XP in Frostborn Wrath can be time consuming. Here's a quick way to get XP fast. Note that this is really only effective for getting from level 50 to level 250ish.

1) After you hit level 50 or so, play the first scenario on endurance mode and beat it. Every time you do this, it will extend endurance mode by 5 or so tiles. Eventually, you won't be able to beat it any more, but you'll have longer endurance modes.

2) Max your orb/banishment skill, if you have it (if not, it helps, but isn't necessary). If you have XP related talisman pieces put them in your talisman (again, not necessary, but it helps).

3) Play endurance on any given scenario - max all your battle traits. It will make it more or less impossible to even kill a monster. That's ok, you're not going to kill any monsters.

4) Stick as high a level gem as you can in the enraging socket.

5) Start every wave as early as you can. Basically, every time a wave starts, immediately start the next one. When that happens, you'll get XP for starting the wave early. You will also get your spells to recharge faster.

6) Any time you get large clusters of monsters, freeze them, and then hit them with your other spells. If you can get 100+ monsters in the range, that'll give a fair amount of experience.

7) After starting all the waves early, pause the game. If there are any buildings you can bomb for experience, bomb them. You should have plenty of mana from starting waves early.

8) The combination of starting waves early, bombing buildings and spells should give you a couple thousand XP for the level. But because you've maxed traits, your multiplier is going to be high. Mine was about 15x. The result is that getting only 4k xp in the scenario, gives you 60k xp!

Until you get to very high levels, 60k is enough to level you up at least once. It takes less than 5 minute to run a scenario using this approach.

9) As you get more levels, you can beat higher scenarios, and will be able to acquire more battle traits. You can then repeat with more battle traits to get extra multiplier and farm even more mana.

There are probably variants to milk even more out of this general approach, but this is a way to get a ton of levels quickly without the drudgery of having to beat full endurance modes. good luck!