Bomb

Illumination. The elemental sheds bright light in a 15-foot radius and dim light in an additional 15 feet.

Water Susceptibility. Taking any cold damage causes the bomb to immediately detonate.

Detonation Charges. Every time the bomb is dealt damage (except psychic or cold), the bomb adds a charge equal to 3d6 fire damage, up to a maximum of 3 charges. After 2 charges, the bomb swells to size large and its detonate radius increases by 10 ft. Being dealt fire damage gives the bomb 3 charges.

Detonate. When the bomb is dealt cold damage or killed, it detonates for 5d6 fire damage in a 20 ft radius and adds any acquired detonation charges. (see above)

Touch. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit:  7 (1d6 + 3) fire damage. If the target is a creature or a flammable object, it ignites. Until a creature takes an action to douse the fire, the target takes 5 (1d10) fire damage at the start of each of its turns.