The enemies that initially appear in each wave are :
Wave 1 : 15 Landers
Wave 2 : 20 Landers, 3 Bombers, and 1 Pod
Wave 3 : 20 Landers, 4 Bombers, and 3 Pods
Waves 4 and up : 20 Landers, 5 Bombers, and 4 Pods
Avoid using hyperspace unless you are about to die. Fighting off attacks, regardless of the number of enemies, will make you a better Defender player.
Baiters can usually be overcome by hitting the reverse button twice quickly. They will fly past you and be in range for your fire power. Do NOT try to outrun them as baiters are faster than your ship.
Swarmers are easy to defeat. You can hit reverse as soon as they fly past you and fly behind them. They cannot shoot backwards so you can blast away at will.
Shooting a Pod will release between 1 and 7 Swarmers. The chances that it will try to release 1, 2, or 3 Swarmers is 1/256 for each. Also, the maximum number of Swarmers allowed in the game is 20. So, for example, if there are 18 Swarmers in the game and a Pod is hit, it can only release a maximum of 2 Swarmers.
At higher levels, you will need to play God and even sacrifice some Humanoids (by killing them yourself) to preserve the rest of the planet's population. The planet is too large for you protect and you are sparing the Humanoids from a fate worst than death (mutation). Do not worry, these Humanoids reproduce quickly and overpopulation has always been a constant problem. The planet will be fully populated at the start of every fifth attack wave (configurable).
The International Date Line : there are reverse lines for Swarmers and Mutants (AKA the 'International Date Line'). If this line is between you and the type of enemy in question, they will travel the opposite direction around the planet to get you (i.e. they won't cross this line to get to you). If a Mutant, say, is following you and you cross the Mutant reverse line (to the left of the big mountain) it will suddenly reverse direction and go around the other way. The same is true for the Swarmer reverse line (located approximately where your ship starts each wave). This doesn't affect Swarmers that you are following behind. If you're on one side of the line and a Pod is on the other and you shoot it open, the Swarmers will fly away from you and you can get in behind them immediately. The best use of these lines is where there are lots of Swarmers and/or Mutants that you don't want to hassle with. You stay near the line and go back and forth over it to keep the enemy on the other side of the planet. This is especially useful in space and waves that get really hairy.
Freeze : you can freeze a Defender machine by picking up all ten Humanoids (on any wave, but Wave 1 is your greatest chance at success), stopping all forward motion of your ship, quieting the screen down (i.e. having no enemies moving around on it) and setting all the Humanoids straight down quickly. This seems to work better were the terrain is very close to the bottom of the screen. Everything will freeze, but you can still move your ship up and down. Thrusting will break the spell, so to speak. If you do pick a spot with shallow terrain, some Humanoids will go thru the bottom of the screen and appear suspended in mid-air near the top. This trick is good to use during marathon games when you've reached Wave 256 and need a breather.
Some top players begin each round by shooting all the Humanoids except for one, which they pick up. The planet is too large for you protect and you are sparing the Humanoids from mutation, a fate worse than death. This keeps Mutants from developing, but it also means that the planet explodes if you lose your last Humanoid. The planet is fully repopulated at the start of every fifth attack wave (configurable). This can be considered an advanced trick.
Due to a bug in the algorithm that computes extra lives, every scoring activity from 990,000 to 999,975 will earn one extra ship and one extra Smart Bomb. If the player suicides on something or gets shot, one ship is lost, but one ship and one smart bomb are awarded; the net effect on the number of ships is zero. Dying on hyperspace re-entry awards nothing, because this awards no points. For winning N ships from 990,000 to 999,975, the player will have to achieve N x 10000 points after passing 1,000,000 before the game's accounting balances, and ships are awarded properly at 10,000 point intervals again. For example, if a player earns 45 extra lives during this interval, he will have to score another 450,000 points before being awarded another extra life. The player gets to keep surplus ships and bombs and can have super long turns where he may bomb two to three times per wave to get out of dangerous situations.
The trick is this: If the player wins 100+ ships between 990,000 and 1,000,000, this causes the game to start awarding extra lives right away again after turning the score over to zero. If the player wins 100 ships, the machine will have to wait 1,000,000 points to begin awarding ships again. However, since 1,000,000 is equivalent to zero, it awards them immediately at 1,010,000.
It's possible on a real Defender machine to make the screen color inverted so that all the black space is white while you are playing. It will reset itself when you die and maybe when you use hyperspace. Smart bomb flashes are cool when it's reversed. The trick was to drop a credit in right when you die and the screen flashes white. Somehow the program gets distracted (non-masked interrupt on coin drop?) and the screen stays white.
Defender attack waves 'roll over' at Wave 100, which is displayed, after being completed, as Wave 0. The game keeps track of the actual number of waves, even though they are not shown properly. For example, the next wave will be counted as Wave 101, even though it shows being completed as Wave 1. The game will 'roll over' again at Wave 200, which is displayed, after being completed, as Wave 0 as well.
The next 'roll over' occurs at Wave 256. Upon completion of Wave 255, the next wave is a 'blank' wave, in which no enemies appear, and the wave immediately ends after the player’s ship appears on screen. This level is counted and displayed as Wave 0, and the player is awarded a bonus of humanoids left X 0 points (the bonus for this wave is always 0 points). The next is Wave 1, and the game now plays just as if the player had started a new game, except the player gets to keep his score and all of his bonus ships and smart bombs.