Space Invaders Infinity Gene

To unlock 'Nightmare' difficulty you'll need to complete all 99 levels in the challenge mode first. The difficulty can be set in the options--->settings screen. You can also set the lives to 9 if you're able. (You'll have to play the game a bit to get the option to select 9 lives, say, complete 'Normal' on easy and then do some of the challenge levels. The game evolves as you accumulate score, giving you more weapons and options)

To make life a lot easier, complete the 'Normal' game on 'Easy' difficulty first and then all you'll need to do is set the difficulty to 'Nightmare' and select the last level, 5-6. I found the 'Field' weapon the best to use and it will make light work of the end boss too.

The achievement will pop when you're getting the stats for the level. Quitting the credits does not matter.

You only need to beat the last level to "beat normal mode" so once you have finished the game on easy go to settings, change the difficulty, & go & replay level 5-6

n.b. This is untested as I haven't actually unlocked Nightmare yet, it did work on normal & hard though.

OK... I have now done this & the method above does work

If you're going to vote down please make a note why so I know what to change.

Thx

p.s. To unlock Nightmare difficulty you need to complete the 99 challenge levels.