Apollo 13 is the game with the most balls during multiball. 13 balls at once is insane!!

Firepower was the first Solid State game with Multi-ball but there were other EMs well before that with Multi-ball.
According to IPDB, Balls-A-Poppin was the first flipper game to feature Multi-Ball in 1956.

I wonder what game has the most multiballs.. It has to be one of the new sterns.

I'm not sure about mechanical issues. I think it just wasn't very fun.

You just can't do much until it gets down to about 5 balls, which is usually pretty quick. IJ's 6 ball MB was pretty obnoxious until you lost a couple. Sometimes, more is not better.

Maybe Ripley's with all the different two balls?

Game with the most different MB Modes?
LOTR has 6 different ones. TSPP has a bunch too. Not sure if one of the newer games such as Lexy Lightspeed have more.
Xmen has 6 maybe 7 if they finished the final wizard mode.

STTNG has 4 different Multiball modes -- Borg Multiball (3 balls), Final Frontier (6 balls), Ferengi (up to 4 balls), and Cardassian (2 balls). Not bad for 1993!

There is also the unofficial "dirty optos" surprise multiball.

Apollo 13 definitely has the most balls at once, but I'm not sure which game has the most multiball modes. It could definitely be Stargate, that game has 8 different multiball modes! The main multiball, Stargate Multiball, Eye of Ra, Sandstorm, and four of the six rounds are also multiball modes.

I've seen a line of balls get stuck in the shooter lane, and the coil keeps firing over and over to try to shoot them out, but when there's more than 4 balls, they are just too heavy for the coil to deal with.