I suggest Helium from my suggestions list.

I also suggest Bismuth (BSMH) rainbow metal which creates rainbow square crystals and it's good-looking decorative material.

Sodium (SDUM). Temperature increases up to 700 C when touching WATR. Creates EMBR and FIRE when reacting with WATR.

Some suggestions:

Francium (FRNC), Decays into NEUT when touching water or under high pressure. Harmful to STKM.

Osmium (OSMI), Very high melting point (+4000 C) but brittle. Conducts heat and electricty better than TUNG.

Radon (RADN), (I know it's a noble gas but it would be different from NBLE), Radioactive gas, diffuses very quickly and produce LEAD when undergoes fusion. (+9950 C/ 245 P) Harmful to STKM.

Lead (LEAD), Solid, Lower melting point than most materials (900 C), resists high pressure. Harmful to STKM.

I suggest unnunoktium (118 element). It's extreamly unstable. Lives only for 2 frames. Looks like EXOT in solid form. Explodes in normal envirioment on NEUT, PROT, Uranium, Plutonium, Lead and Radon (from earlier comment), THDR. Generates high preassure and 10000*C. Sometimes creates SING, VIBR or EXOT. It becomes more stable in negative preassure (<-200.00) and low temp (<-270*C).

Other reactions - unknown

docRoboRobert You know that the name changed to Oganesson

Umm... nope. Good to know, but when?

@TPT_PL: It becomes more stable in negative preassure and low temperatures. It can be usefull with bombs and space simulation, or for "Break that wall challenge".