Players

I have this habit, of sending god level threats at my players using homebrew characters. I've been thinking of sending an actually dnd monster at them, but I need help deciding which would be the best. Any monster works, their level five, but one of them figured how to make clones, using a loophole in one of the classes. Can anyone help?

You'll need to be more specific about your campaign and your characters, if you want more specific advice.

If they are playing a homebrew character and can break the game through a “loophole” (and I would argue there is no “loopholes” in homebrew; just poorly designed content), that is a failing on you as the dungeon master.  You are the ultimate authority on what can and cannot be played at your table, and it is ultimately your responsibility to ensure parity between players and content that is not balanced do the level.

This also makes it nearly impossible to provide you any guidance.  Once you have allowed “level 5” to lose all meaning, we now have no context for what works for your table.  If it were a normal group of level fives, I would feel comfortable throwing a solo CR 10 or a couple CR 7-8s at them for a hard encounter when they’re fresh on resources..  but who knows if that would be hard for your table now that you tossed out the rulebook.

Quote from I_StoleTheLastExoticButter >>

I have this habit, of sending god level threats at my players using homebrew characters. I've been thinking of sending an actually dnd monster at them, but I need help deciding which would be the best. Any monster works, their level five, but one of them figured how to make clones, using a loophole in one of the classes. Can anyone help?

 
This may sound horrid, but it's based off of my experience with DMs who allow extensive homebrews - don't homebrew player options until you understand the game design thoroughly.

If I can explain, most DMs I've met who are keen on homebrewed player options tend to have a limited understanding of the game. Their understanding of how and why the mechanics work (or don't) tends to outstrip the design abilities of those making the homebrews. D&D like all systems isn't perfect, but it has a tendency to break outright when people attempt to homebrew. For example, if you're running 5e are you running the adventuring day? Are you setting out to diminish the resources (spell slots, manoeuvre dice, bardic inspiration etc) between combats? Or are you instead allowing long rests between big battles? You see, if you're running 5e and not running the adventuring day you're already at a point where the ruleset and mechanics don't just creak - they break.

Now 5.5e has thrown adventuring day out of the window, but much of it actually still applies. What the loss of adventuring day tells me is that the designers expect that difficulty in 5.5e comes in a single fight and that they don't expect 6 encounters per in game adventuring day. They expect us DMs to throw one big challenging fight at the party per in game day. Maybe we'll throw in a second, but really the idea of sapping the resources of the party is lost along with the idea of the adventuring day. Note here I'm not commenting of if this is good or bad. That's not the point. If you're running 5.5e, then it's a little more tolerant of homebrew because much of the restriction of 5e has disappeared. What a DM then needs to do with 5.5e is to ensure nothing more than maintain the advantage that the players have over the enemies.

The most useful advice to give though is this: if you need help deciding what monsters to throw at your party, you shouldn't be allowing homebrew at your tables. You Simply don't have a strong enough grasp of the game you're attempting to modify. It's like trying to fix a TV with only the basic knowledge of how to wire a plug - it won't end well.