Sometimes, games are only as great as the challenge they present to the player. Whether that be a perfectly timed set of jumps, puzzles that melt the mind or maybe even stealth sections that require precision movement to conquer.
More often than not, if it isn't any of the above then combat is what will no doubt present players with a challenge - sometimes this can prove to be more engaging to tackle for hours on end.
Though a lot of the time these enemies are introduced later on to derail the player and kick them out of the gameplay loop, sending them spiralling out in the hope they'll lick their wounds and try again. However, that's all well and good in concept, but these enemies serve no other purpose other than to infuriate players time and again.
10. Glasp - Resident Evil Revelations 2
There is a special place in hell for any enemy type in games that is - or can turn - invisible. Something about them either seems overly frustrating or just plain cheap. Unless it's literally the Predator, invisible enemies need to get out of games altogether.
Resident Evil Revelations 2 is guilty of such sin, when the Glasp is introduced midway through Barry's campaign when these disgusting, bulging fly-things infect some of the darkest sections of levels. These things are invisible to the naked eye, but Barry's partner Natalia Korda can spot them with her gift that allows her to see infected from afar. This doesn't help when in certain sections, Glasps will be spawned behind the player, and if they get too close, it's a one-hit kill.
Add on top a really gross death animation, as the Glasps literally poop bugs into the player's chest.
When playing as Barry you'll have a chance to know one is near as the screen becomes a blur hindering line of sight, but none of these encounters did much for Revelations 2. There was much criticism over the first Revelations for lack of enemy types and combat becoming a bit stale, but these bugs were just a straight up pain.