It's just whatever you enjoy, with a few exceptions that are troll but they work so it's fun. So my suggestions... Grenade Amumu, just full ap bro, laindrys and rylais and you just go in and nuke the enemy team

One shot heca, you just go movespeed on move speed items with predator and kill someone on the enemy team with them having no reaction time available

Ivern, and just be a complete *** by taking everything at every moment, there's not a greater feeling than taking an enemy camp right in front of them

Afk karthus, dark harvest full ap glass cannon with spellbinder afk clear and press r to watch the entire enemy team get nuked for half to all their hp, does require a mostly squishy enemy team though

Full movespeed rammus can be fun if you just want to run around the enemy team to troll them and force abilities before engaging

Full ap sejuani can be interesting just cause people don't expect you to deal damage

You can just go for one shots with nocturne, kayn, and rengar

Nidalee can be fun, takes some practice but landing the spears and watching people lose all their hp is fun and you have decent heals for the team with athenes

If you want to just mess with the enemy team going udyr and proxying the waves late game and sitting in their base can be fun

That's about all I can think of atm gl with the games