Mars Matrix - Platform: Dreamcast

Easy money
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Buy Score Attack 3 in a shop, then go to arrange mode A and 
select Score Attack 3. Choose the Mosquito 02 (the blue jet) 
because it is much faster then Mosquito 01. You will die in 
the game will have unlimited lives. No matter what happens, 
keep pressing R and collect as much money as possible. At 
the end, return to the shop and check how much money was 
collected. If not enough, play it again until you get enough.

Try to buy the Speed Option and Score Attack 4 in the shop. 
Then make it fast for your jet, by going to Special Option. 
Go to Score Attack and choose "Arrange" mode. Then select 
Mosquito 02 (the blue jet) so you can move fast. Kill 
everything in sight pressing or holding R to get even more 
money. Do not worry about dying because you will have unlimited 
lives while playing.

Buy Score Challenge Stage 3 and then play it under Elite 
Mode A. Go though the level, collecting as much money as 
you can. Only use your Piercing Cannon (press R) because 
you get more money. Do not worry about dying, because you 
have unlimited lives. When you get to the Boss, position 
yourself over his center and use your Piercing Cannon. 
The gold will come pouring out.