The Giant Cape adds 20 HP to the Pokmon it is attached to, while the Rocky Helmet inflicts 20 damage each time the Pokmon is attacked
Another perfect example of this is Isshin, Two Heavens As One, which reads: "If a creature attacking causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time." This is an incredible ability to have on a commander - and building a Commander deck around it is sure to be a blast - but in a Standard set it just feels off
Like The Meathook Massacre, it's unsurprising that this one has found its way into Historic as well as Standard
This is just an example of core too, dont follow this as the absolute truth, for example, many people dont play Bystials, Scattershot, others play Heartbeat mainboard, other dont play Dweller in the main, etc
For trading cards, theyre a liability