While it’s tempting to complete each World as quickly as possible and move on to the next, some patience is advisable:
In the early stages, when you haven’t yet completed all the worlds, you will often find yourself short of Coins, so the 50% bonus in your last world is really useful. Because each world gets more difficult (haven’t quantified it yet, but you can get some idea from the Boss HP in the Bestiary), when you start a new world you will not get far, and even though the coin drop rate increases, your earnings will decline - and if you go back to the previous world to farm coins, you won’t get the bonus.
Specifically,
- Don’t complete the level using a Revive, paying 150 gems (this is never a good idea unless you are throwing a lot of money at the game), or getting the lucky chance ad (although you could still use it to get a little further along, especially for unlocking rewards for the intermediate bosses)
- When you think you are ready to move on from the current World, skip the Mystery Crates
- You should be able to complete the level even if you don’t get the perks you want (e.g. can you do it without multi-shot?)
In the past, when Pirate Ship was the last world, some players purposefully didn’t complete it to retain the 50% bonus, but eventually the game was updated to retain the bonus on the last world in the game even if you have completed it.
That said, you shouldn’t unnecessarily delay and stay at a lower world, because
- Equipment and upgrade material drop rates are better in higher worlds
- You gain a lot more XP in higher worlds
- You unlock 2 new perks every time you unlock a new world
- You gain more coins in higher worlds (but not a significant amount)