so i created a really strong sommoner/conduitions/a bit of damage. the thing is he might be to strong with a dragon orb tons of rings and 70 ac. how do I prepare the players?

Just pick an appropriate creature from the monster manual and reskin it to be your summoner. Life will be easier for everyone.

Even without saying what level you're making this for, I can already say, yes, you've gone way overboard. Even if we just look at the AC. The highest AC any official monster has in 5th edition is 25, and you're going all the way to 70. This game is designed around more tightly controlled numbers; look up "Bounded Accuracy" for the full definition and design logic.

Check out monsters at the appropriate level you're aiming for, and base something off of one of those.

a misty hologram monologuing uninterrupted as swords pass right through him is equally unkillable as 70 AC but without the... i don't know what to say. without the "i like to burn ants with a magnifying glass" vibe, i guess? if you simply must have a relentless force of unnatural menace, then maybe throw an inexhaustible tide of zombies at these players. the edges of it are something the characters can interact with even if their actions never quite put a dent in the overall mass. there's drama and action and people trying clever things...

but you're not asking what to do differently, you're asking how to prepare the players. i'd recommend you bring pre-printed coloring sheets and crayons so they can pick your guy's wardrobe while you describe all the cool loot he's wearing that they'll never have. i mean, this is just godly dress up fun for one person with a captive audience, so why not lean into it?

I mean, highest possible AC is 30, attunement applies to bad guys as much as players, and summoning kinda sorta takes time to sort out, especially if one chooses not to use a circle because they got better things to do than be someone’s play toy.