Monsters keep coming in waves, and the only way to keep up is to make your weapons stronger than they are. Merge And Fight is an action-survival game in which you dodge through the horde while combining gear into better gear, until the boss of the stage finally shows up.
The trick is to merge between dodges rather than standing still to sort your gear, because the monsters never wait. When you need a breather from the crowds, Classic Snake offers a quieter kind of survival.