The term "bullet sponge" refers to an enemy character whose health and damage resistance is so great that it becomes the single most important quality when describing its difficulty level. Instead of incorporating clever AI or divergent behavior, the enemy will repeat the same basic attack patterns and wait until you've expended the necessary amount of bullets to reduce its health to zero. This effect can be particularly disconcerting when fighting an unarmored human opponent and they shrug off high caliber shots to the head as if they were rainwater.
Examples[]
Borderlands[]
The amount of damage that you can output is directly tied to the ratio of your level in relation to your enemy's level. If you happen to find an enemy that is a much higher level than you, your only two options are to run or die. The only way to defeat higher level enemies is to first grind the experience and money on lower level enemies to level up your character and unlock higher level weapons. What's most disappointing is when higher level enemies are just a differently-colored version of the lower level ones with more health and higher damage output.
Tom Clancy's: The Division[]
Instead of offering a greater variety of enemies for the players to fight, or better AI for tougher foes, The Division instead falls back on bullet sponge enemies as bosses. These are simply normal enemies with normal behaviors but with a ridiculous amount of health. These bosses in particular take many magazines' worth of bullets from multiple players to take down. Despite this, they offer no extra challenge because they have normal AI behaviors, and are simply a waste of time.
