After realising the Moon Lord's colour palette only matches the Vortex Pillar, I think it'd be kinda fun if the Moon Lord had 4 variants it could spawn as, each focusing on different attack patterns.
Solar Moon Lord dealing out more melee attacks, being tankier, but also a bit slower so he's easier to dodge.
Nebula Moon Lord having more emphasis on attack variety, with lots of new effects like curving lasers and new attacks, but longer cooldowns between them.
Stardust Moon Lord doing way more summons, but taking damage as you defeat summons too, perhaps tentacle whips.
Vortex kinda just being regular Moon Lord we have right now, since it's got a ton of ranged attacks and lasers.
idk, spitballing here, might mod it some time
Actually, there's a stronger contender there. Flask of nanites which only inflicts confusion on some enemies.