Mr. Heli is a scrolling blaster that scrolls from left-to-right, but also moves down. The conversions by Firebird are split into three main stages, although there are mini-levels within each stage.
As with most arcade shoot 'em ups, the plot behind the action doesn't really matter. Outside of the original Japanese text, the story didn't make much sense anyway! If it moves, you shoot it. If it shoots at you, you avoid the bullets. If a blue crystal appears, try and collect it (for money to then buy new weapons and so on).
Blasting rocks (with missiles or bombs) produces crystals that gives the player money, but only if they can collect them. Sometimes, crystals fall from above and the player has to swoop in to collect them before they disappear off-screen below.
Collecting crystals isn't the only thing the player has to do. The money gained from the crystals is spent in various 'shops' to upgrade weapons and give Mr. Heli other advantages. Upgrades include increased bullets, missiles, shields, petrol (for energy) and fish (to blast through walls - obviously!). Each shop only sells one item and once it's bought, the shop displays a Sold Out sign which prevents the player from buying more of the same.
Of course, flying enemies are out to get Mr. Heli, including spy choppers that can steal various upgrades from the player upon contact. Mr Heli has to shoot 'em all!
The end of each section or stage involves battling a large boss, often protected by other cohorts as well as an array of weaponry.
Mr. Heli includes an annoyingly catchy tune (taken from the coin-op) in the 16-bit versions. The original tune was released on a music CD (along with a number of other IREM game tunes) in Japan.