异形 血 机甲 第一人称射击 死亡 机器人 open-source 跑动射击 Steam backtracking 成就 时间限制 变种 在线 陷阱 夺旗 esports 彩蛋 传送 续集 沉默的主人公 swimming one-man army clan 查看全部 + darkness BOSS 战 爆炸 死亡竞赛 数字发行 Steam 云记录 多人分屏 倒计时 语音出演 人类 game reference wasd movement extreme violence corpse grapple 实时战斗 underwater gameplay 地图编辑器 secret area shielded enemies 困难关卡 self-referential humor quicksaving mercenary developer cameo moving platforms sequence breaking multiplayer scoreboard been here before tentacles temporary invincibility mod support multiplayer lan zero point achievements griefing camping splash damage gore system CD invisibility vent crawling bots severed limbs 上帝模式 secret areas within secret areas alien languages strafe-jumping selective invincibility pc to console port team killing playstation mouse support e3 1997 source port dial-up wide area network game operation interactive achievement awards 1998