The 'official' Twitter for weird gamesoft review site, Gaming Hell! The old game site with guts! Huge guts!! Sarh is our mascot! Author: @TepidSnake
Before we get started, this is NOT a definitive list of all non-physically released games, all essential games to get or anything like that.
The arcade Bucky O'Hare is notable for basically serving as a finale to the cartoon series, which only had one season and never really had a final 'defeat' for the bad guys, the Toad Empire.
However... There are three versions of Mad Father. The very first one, from 2012, is freeware and still available, with a translation by vgperson
"Hey, aren't there normally more screenshots with these tweets?"
The PS1 port of MvC is, needless to say, very compromised, but they tried their best. Performing a Duo Team Attack, for instance... Brings in a ~clone of your opponent~. Don't need to load a partner into memory if they're already there! 
Uncovering some of the Deep Lore about Bug Panic, it appears to have its roots in Cave's feature-phone output, a game called Mushihimesama Gaiden (虫姫さま外伝) which plays very differently but seems to be where Reco's sprites in Bug Panic come from. 
A JP MUGEN Wiki & other places have a page looking at two of the game's characters- Arabian Moon and Broadway / Cattydox, but no source.
Ah, remember when Nintendo rereleased SMAS on the Wii and, just to crush the spirit, made sure it was crystal-clear this is exactly the same as the SNES game ~and~ in 50hz because get stuffed, PAL-Landers? Ah, good times.
Why did I say 2007? I need to put my glasses on, what I totally meant to type was 2002.
There are some arcade Data East rereleases out on Switch like Joe & Mac and Bad Dudes, but these are by Flying Tiger Entertainment under the Johnny Turbo's Arcade name- yes, the TurboDuo mascot from the '90s- and their quality is dubious at best. Some are OK, others are ~rough~.
American readers probably remember that Kangaroo was brought over to the US by Atari, and so it was one of those games you could get pin badges for from them. They were sold at arcades for promotional purposes, as outlined here:
Bad jokes aside, Vampire Night is a bit of an oddity. A collab between Namco (on their System 246 hardware) and Sega's WOW Entertainment, it's almost a halfway point between The House of the Dead 2 and 3 as the boss life gauge from 3 was introduced here.
Back on some OutRun 2019 stuff, and the prototype Junker's High is known for having SRAM support, saving your records and replays. This was stripped out of the final game.
Let's have a look at that teaser image again... Ah, yes, there's Zeke, all the way to the left! 