Hi there slime slayer,
I will be direct about this, online multiplayer is getting delayed with no ETA for now. The Slimeking's Tower was created as a single player experience from the very beginning, and it's being under development for about 4 years now, this means that it's optimized to work as a single player game, and as you might have heard before, adding multiplayer to a singleplayer game is no easy task.
But multiplayer is so cool, so I worked hard during months to bring online multiplayer to The Slimeking's Tower, and I actually did it, as shown in the video that I'll leave below. It took a really (and I mean REALLY) long time to get every item (+ synergies), character, pickups and enemy working, and every element works flawlessly on his own, but when you put everything together this happens:
https://www.youtube.com/watch?v=Pu_UhaWCWKo
You might notice some stuttering, wrong colors and missing fx, but that's just lack of polish that was supposed to be added these days. The real problem are the desyncs, you can notice at the very beginning of the video that some monsters stop moving for a split of a second then continue and despite looking really bad, that could be "easily" fixed with some smoothing, but the real problems start when a lot of stuff is happening on the screen.
At about 1 minute into the video you can notice some severe lag and the desyncs start to happen, leaving some monster bodies behind in the guest screen (the right one) while they are dead in the host screen (the left one). I won't go into much details about why this happens, but that's why I said earlier that this game wasn't thought with multiplayer in mind, so the engine is very good working with everything that happens on the screen, but it's atrocious telling what's happening on the screen to another player, it needs to send and receive tons of info and it's just not able with keeping the game in sync.
So this it's not a f*** multiplayer, it will be added to the game at some point, but that requires a major rewrite of the game's code, which is really time consuming and this game is developed only by myself. And a lot of cool stuff is planned like the RPG Mode, which takes priority by now over the multiplayer.
And that's all, I'm really really sorry to write this, after working on multiplayer for many months now, but it's just the way it is.
Also if you made it this far, the 1.5 update is coming out this 25th of May, surprise!