I have som suggestions for elements and mechanics. It will be mostly about explody things and things helping in making bombs.
Elements:
SMTR - strange matter - Explodes on contact with PROT. Could be created in small amounts from exploding EXOT, VIBR or BVBR. Like EXOT, SMTR has many strange and odd reactions, such as:
-turning into PROT on contact with NEUT
-turning WATR into ACID and WTRV into CAUS
-more being created on contact with PHOT
-makes WOOD spontaneously combust
-turning SLCN into COAL or BCOL
AMRA - anti-matter resistant alloy - Works like INSL, but with the added benefit of being resistant to AMTR. Could be useful in making anti-matter bombs. Could be created from EXOT and SMTR.
EXGS - explosive gas - Explodes with larger power than GAS. Could be created from HYGN and GAS.
Mechanics:
If AMTR is in contact with any element (exept AMTR, AMRA, CLNE, PCLN, DMND), it destroys itself and the pixel it touched and it heats the surrounding elements to very high temperatures (around or above 8000C) and creates high pressure (>15 pressure), in the process creating 2 PHOT with the same temperature (around or above 8000C).
PLUT slowly decays into URAN (about 0.5px/min) witch also slowly decays into POLO (about 0.25px/min) (and yes i know this could lead to infinite fussion)