Probably a shark? I mean as soon as you said night time paddle our I thought 'that's dumb sharks feed at night'. You're not supposed to snorkel at night because you're on the surface. Scuba is okay because you aren't on the surface.I went to the gulf of Mexico with several buddies about 20 years ago when we could camp on the beach in tents.
After a day of drinking beer it got dark and my buddy and I weren't up to partying at the bars anymore with the rest of the guys. It was still pretty hot out at 10pm so my buddy and I decided to wade into the ocean on our boogie boards. As we paddled out the lights from other camps got dimmer as we got further from shore.
The ocean was dark and calm and paddling further out became kind of a game of chicken competition between my buddy and I. We were talking about the days events sipping on Coronas, floating 15 to 20 feet from each other when something bumped my board from underneath.
I was about 240 pounds and it pushed me a foot or two in the air. I was surprised by the bump but feeling pretty chill from a day of drinking. I called my buddy an a-hole for kicking my board and he didn't say anything. It was like someone trying to dump me off an air mattress in a swimming pool so I figured it HAD to be him messing with me.
Without saying a word my buddy started paddling toward shore and I followed him. He gradually increased his speed and even though I tried to get him to slow down he wouldn't stop. Eventually we made it to shore and back to camp, my buddy never said a word the entire way.
When we got to camp I asked him what the hurry was, he said with big wide eyes "I didn't kick your board dude". I asked him if he didn't did he see who or what did? He said don't worry about it. I tried to get him to tell me what he saw and he never spilled the beans. I know he was too far away to have kicked my board.
I lost touch with that guy years ago but still wonder what he saw that caused him to paddle to shore so fast and appreciate that he didn't tell me the full story and cause me to panic when we were floating a quarter mile from shore.
He was a scuba diver so I don't think a dolphin or seal would have alarmed him so he must have seen something pretty sketchy. I tried to bring up the subject a few times with him years later but I felt like whatever he saw left him with a little PTSD or something so I stopped asking.