Note that “Heavy Mech Support Platform” is different from other Union Monsters in that its last sentence is applied if the monster it is equipped to is destroyed (period), not just when the monster is destroyed as a result of battle. This extra effect does not apply to previous Union Monsters.
If a monster equipped with “Heavy Mech Support Platform” is targeted by “Ring of Destruction”, then “Heavy Mech Support Platform” is destroyed instead of the equipped monster, and the damage inflicted to both players by “Ring of Destruction” is 0 (because the monster targeted by “Ring of Destruction” was not destroyed by it).
If you have a monster, “X-Head Cannon” for example, equipped with “Heavy Mech Support Platform”, and you activate “Limiter Removal”, the ATK will becomes (1800 + 500) x 2 = 4600. Also, the “Heavy Mech Support Platform” will be destroyed instead of the “X-Head Cannon” during the End Phase (by the effect of “Limiter Removal”).
If “Heavy Mech Support Platform” is equipped to “Big Core” or “Reflect Bounder” and they would be destroyed by their effect, “Heavy Mech Support Platform” is destroyed instead.
If “Reflect Bounder” equipped with “Heavy Mech Support Platform” is attacked by “Dark Ruler Ha Des”, during damage calculation “Heavy Mech Support Platform” is destroyed instead of “Reflect Bounder”. Then, after damage calculation, “Reflect Bounder” will destroy itself by its own effect. Its effect is not negated, because it was not destroyed by “Dark Ruler Ha Des”.