Though bedtime isn't a time for games — you want your baby to understand that it's time to sleep, not to play — the bedtime routine or any other time when you want to interact with Baby and have quiet fun with her is a good time for the relaxing fun of quiet games.
You can play one of the traditional games, such as “Where Is Thumbkin?” or “Here Is the Church, Here Is the Steeple,” or you can make up one of your own. Quiet games are just that: quiet, relaxing games that won't get Baby revved up. If this is a prebed or prenap game or a game at any time when you want Baby to relax, then it isn't the time for hiding below her vision level and popping up and saying “Ah,” “Boo,” or any other such excitement. Even a demure version of “Peek-a-Boo” with you merely holding your hands up in front of your face or hers to block her vision of your face is inappropriate here.
Mobiles are popular with babies and their parents, and indeed they keep many a baby amused in his crib. Though watching a mobile may keep your baby entertained quietly until he falls asleep and watching it may be hypnogogic (sleep-inducing), you don't want the baby to get accustomed to having the mobile going 'round and 'round. If he isn't yet asleep by the time the mobile has run down, he's likely to start crying until you come in and rewind it.