Anti-Bayonetta tips

1) Face back often if your character's Back Air is standard fare
The reason for this is because standard Back Airs are your friend. The standard Back Air will be an extended back-kick, which provides both power and reach. The former allows for burst damage and the latter can hit the opponent unexpectedly. Bayonetta particularly wants nothing to do with dealing with either one. Now she can still Witch Time, but a standard Back Air works as a psychological weapon against it because of the reach and can set up for a Forward Smash or Grab this way. Just make sure you won't mind the loss of Back Air access until you can face back again if you will go ahead and use something else to attack.

2) Focus on HOLDING the center
Grabbing the center is desirable for the space, of course, but getting complacent with center control against Bayonetta is a good way to run afoul of WT. Holding the center means that Bayonetta has to eventually attack. She can't roll between sides either because her rolls have terrible range, so direct combat with you will be inevitable, and staying around the center will help make sure it happens on your terms.

3) Set up anti-aggression traps
Witch Time--and in fact, any Counter move, really--has a subtle weakness: the user's mobility momentum drops sharply. An attack placed where it would hit the user ONLY if they don't use the Counter move is great for drawing out the Counter move and likely punishing it, and any time Bayonetta thinks twice about using Witch Time because it also stales makes her increasingly more likely to use her rolls with all the problems that can easily come with it.

4) Bullet Climax is something to consider for an entire given matchup. Do so ASAP.
Some characters, like Jigglypuff, can outmaneuver BC with immense ease when they are in the air, and this will make doing everything else significantly easier for them. If you're a character with bad air mobility and/or high height, don't expect to be so fortunate. Make use of crouching if you do want to be closer as any such character, because even if you still get shot, BC has cooldown issues while the crouching will keep you from being stunned as long. With the right position, you could manage to strike back with a vengeance.

5) Stay wary of the Side B
In its own right, Side B is a persistent threat. It can't burst KO, but it can be used to provide grief against your momentum. If you can't simply go in the air to prevent it from working nearly as well, use your dodge moves so that Bayonetta can't use it carelessly because you could get an unexpected position advantage. Naturally, you still want to go in the air, so see 4 because Bullet Climax is the primary factor against that.

6) Above all, never panic
Bayonetta doesn't have a lot of net power in general behind her. She can rack up the damage, but her kill moves are few and far between and ultimately easily identified. When her nastiest traps are disarmed, Bayonetta is bound to be the one panicking, and that will do her no favors.