Hello. I'm not entirely sure if this is the right place to do this, but I just thought I'd report a bug.
I couldn't spawn the Crystal King in multiplayer. I made the summoning gem, walked over to the fountain, and right clicked it. The gem icon showed correctly on my mouse, the summoning gem was consumed from my inventory, but nothing happened. No boss, no music change, no message in chat, nothing happened except the gem dissapeared from my inventory. I tried a couple of more times, but it just ate more of my boss summon gems without spitting out a boss.
Went into singleplayer a bit later to test whether the boss would spawn there, and sure enough, it worked without issue. Boss spawned just as expected, behaved as expected, dropped stuff as expected. So this is purely a multiplayer issue.
Other mods I'm using are: Thorium Mod, Fargo's Mutant Mod, imkSushi's Mod, Recipe Browser, MaxStackPlus, AlchemistNPC, Fishing 2.0, Helpful Hotkeys, MoreAccessories+, Shorter Respawn Time and Boss Checklist. (The boss doesn't show up in Boss Checklist either, by the way. It'd be nice if it was compatible with that.)
Terraria version: 1.3.5.2
tModLoader version: 0.10.0.2
Thanks for the great mod overall, though, and have a nice day.