Aetherflux Engine

Aetherflux Engine enters the battlefield tapped.
Aetherflux Engine doesn't untap during your untap step unless you pay {5}.
Whenever you lose unspent mana as steps and phases end, put that many charge counters on Aetherflux Engine.
{5},{t}: Add {x} where X is the number of charge counters on Aetherflux Engine.