Snowball: Snowball will give you 8 snowballs to knock other players off. Note: The snowballs disappear after the end of the round.
Speed Boost: This will give you speed 3 instead of speed 2 for a few seconds.
Teleport: This will teleport you to a random player.
Invisibility: This will give you invisibility for a few seconds.
Shield: This will give you a shield.
Random: This will give you a random powerup: Note: You may also get blindness or nausea.
Deathmatch is at the end of a game, when there are only 6 players left. After the end of each round, all the players will be teleported to spawn. This is due to people not being able to find others during the endgame.
Hit glitch, as people call it, is not actually a glitch. It was implemented to mess up timers. The more people there are, the percentage of getting a hit glitch is higher. This could be very annoying as it could kill non-timers as well. I'll bet you you've had a game where hit glitch killed you.
Timers are a type of player who wait until the last second to tag a player. Many people hate timers, as they are very annoying to some and many people think that this is a cheap strategy for noobs.