Levels / XP

Player level determines two main things: the amount of units you can have on board at a time and the odds for your unit shops.

The number of units you can have on the board is equal to your player level added to the number of Force of Natures that you have.

At higher levels, the likelihood of getting higher cost units increases while the likelihood of getting lower cost units decreases.
Check here for the odds at each level. https://lolchess.gg/guide/reroll

How to level

Your player level increases once you hit certain EXP thresholds. After every round you naturally gain 2 exp.
This can be accelerated by purchasing 4 exp for the cost of 4 gold.

Level thresholds

3: 2 EXP
4: 6 EXP
5: 10 EXP
6: 20 EXP
7: 36 EXP
8: 56 EXP
9: 80 EXP

Due to these thresholds, you typically end up with specific timings that are ideal for purchasing exp. These timings are distinguished as preleveling, leveling on interval and leveling off interval.
Preleveling is when you purchase enough exp so that you will level up naturally on the next round in order to adjust your odds towards the higher cost units.
Leveling on interval is when you purchase exp so that you end up perfectly at 0 EXP after hitting the leveling threshold.
Leveling off interval is when you purchase exp and end up at 2 EXP after hitting the leveling threshold (uses up 4 extra gold for the same level). This one is typically done to maintain the standard leveling tempo of the lobby/when you don’t need to roll for anything/all-in.

Standard leveling times

These do not necessarily apply if you are playing reroll comps/open fort.
1-3 Prelevel to 4
2-1 Level to 4
2-4 Prelevel to 5
2-5 Level to 5
3-2 Level to 6
4-1 Level to 7 (off interval)
5-1 Level to 8 (off interval)

Other common leveling timings

These level timings are usually for maintaining win streaks/playing aggressively while improving odds of hitting high cost units naturally.
3-1 Level to 6 (off-interval)
3-5 Level to 7
3-7 Level to 7
4-2 Level to 7
4-5 Level to 8
4-7 Level to 8
5-2 Level to 8

Uncommon leveling timings

These tend to be lower value since you only stay higher level for at most 2 or 3 rounds while losing a lot of interest in exchange but occasionally is the right play.
2-2/3 Level to 5
2-5/6 Level to 6
3-2/3 Level to 7
4-2/3 Level to 8