I think that Wario is a soft counter to snake.
if they recover too low, you bite them. if they recover high, but not too high, you can waft/super waft.
we severely limit his offstage options with the bite, and then we have a high priority Uair to pester him with when he tries to Dair/Nair or FFAD to the ground. YOu can juggle a snake for a good minute, he has trouble getting out of it. Uair beats both his Nair and Dair(ftilt also beats his Nair if they try to space you from the air), not sure about his Bair though....
For the mortar slide, if you predict it, you can Fsmash, or pivot grab works fine too (i suggest dashing away and pivot grabbing, that way you will be less vulnerable to his mortar as it comes down, though if you dash grab him fast enough it won't even come out, but seeing as Wario's dash grab is ten frames, and his pivot grab is eight, pivot is a better frame option, and easier to time, IMO), but most times I will pivot grab so that way I can have more time to decide how to **** him position-wise.
if you are a beast and they are near kill percents, you can half-waft him out of it and it will kill super early (60-80% if it surprises them near the edge)
for tilts, it's not that hard. you can just play Dair games and camp him. it's pretty easy to camp snake since all his projectiles aren't as fast as say, toon links. and you can shieldgrab his Ftilt. but sometimes snakes will try to beat your dair with thier Utilt, so what you do is you float above them and bait it, then either dair to their other side and jump away, or stay inside and try to get a grab, or reverse bite them, or fsmash if you think they will try to atttack again, maybe charge it if you think they will spotdodge. I think I covered all their options lol.
that about covers everything I have to say, except to stay away from his projectiles, don't get baited into running into tilts, don't fall for C4 traps ( if you see snake trying to C4 you, hit him or get to the ground and shield/spot dodge before it goes off, but the best alternative is to just not get stuck in that position) and keep him in the air/ off the stage.