The best casual games like Super Smash Bros are Rivals of Aether, Brawlhalla and Nickelodeon All-Star Brawl 2. Below are 6, each with the reason it is here — and, at the end, what filtering to casual costs you.
Filtering to casual means you want something you can put down. That is the whole definition, and it says nothing about how deep the game is.
What you get: A game that fits around a life. Short sessions, save anywhere, no penalty for a week away.
What made Super Smash Bros worth playing in the first place is covered on the full list. This page is the casual part of that answer, and only the casual part.
The competitive answer: platform fighter built for tournament play.
Free, cross-platform, and the easiest way into the genre.
The closest mainstream alternative with a real roster.
Platform fighter built around 2v2 team play.
Sony's attempt — different KO system, worth it for the roster.
If it was the party chaos you wanted rather than the fighting.
Momentum, sometimes. A game designed to be left is also a game that is easy to forget you were playing.
Specifically, these are strong answers for Super Smash Bros that are not casual games, so they are not on this page:
The full list is on games like Super Smash Bros — 9 picks, no genre filter.
Rivals of Aether. The competitive answer: platform fighter built for tournament play.
No. Super Smash Bros released on the Nintendo 64, but a recommendation is only useful if you can play it, so the picks above span platforms and eras. What they share is the genre and the reason.
No. Several of the deepest games there are — Tetris, Balatro, Into the Breach — are playable in twenty-minute pieces, and some of the shallowest demand an entire evening.
Often the opposite. Many are built around daily timers and streaks, which means stopping does cost you — the one thing a casual game is not supposed to do.
By hand. Each pick was written for the full Super Smash Bros list first, on what the game actually does, and this page is the part of that list that is casual — never a genre tag lookup, which is how "best racing games like Super Mario 64" used to be a page on this site.
Or read the casual guide for where to start in the genre generally.