The maintenance screen mostly shows when there are too many people on the server. Usually, you can just refresh your page to get out of it (and in the game).
If you want Vollo Brightbloom, don't get him in the shop for 30 PC. Starter Pack 1 (on the home page) has him and a bunch of other stuff for 25 PC combined.
To solve the problem of useless XP and not enough hero HP (later on), the makers could let the leftover XP from other units be converted into HP for the hero. + if you agree.
To solve the problem of useless XP and not enough hero HP (later on), the makers could let the leftover XP from other units be converted into HP for the hero. + to let the makers see.
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 "Hordes and Lords")
 "Legacy of a Thousand Suns")
 "Bloons TD 5")
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 "Epic War 5")
 "King's Guard")
 "Road of the Dead")
 "Bloons Tower Defense 4")
 "Burrito Bison")
 "Infectonator : World Dominator")