An assortment, very Mind-centric!

Heart specifically has a shotgun. It's usually loaded with buckshot, and one of the pellets did hit Mind he just hid it bc he doesn’t want Heart to have the satisfaction of having hurt him. Soul confiscated it after the Juno incident and Mind stole it and almost killed Heart with it at the very end of TME (which is what finally pushed Soul into action for TSE). After that, he kept the weapons in a much more secure arrangement.

Soul has wings! Bat/demon wings, as opposed to Heart's bird wings. They're smaller and lower down, so they're not very viable for flight, but he'll gesture with them a lot of the time.

Mind got jealous of HS having bonus limbs so he gave himself 2 extra arms below the ogs and said it was for convenience. But he didn't plan ahead with how clothes interact with the extra arms, so he usually has to wear crop tops or modify whatever he wants to wear to accommodate them. He swears up and down it's on purpose and he knows what he's doing, but if Heart wants to annoy him he'll give him nice clothes that are a hassle to modify and/or slip weak magnets in inconvenient places on clothes he needs to modify, because later he'll have trouble with precise movements near the magnets

Mind stole Soul's trident to blind Heart as revenge for destroying his arms in The Man With The Skeleton Arms, unaware that it was an accident. That's why he has mechanical hands, he had to replace them. Over time, he kept replacing parts of himself with mechanisms, and now he's got a screen for emoting with his face when he feels like it.

The right half of the facial screen actually glitches sometimes because of the Juno Incident, linking back into my first hc. When it glitches he looks like biblically accurate Mind from the album cover. He's tried over and over again to repair it, but nothing has worked. He doesn't like that it's the only "scar" he can't get rid of, so he pretends the glitches are intentional

Headcanon #561