I won't touch the actual effects or balance, but they haven't made cards with persistent pump effects like described since like 1999. However, there is at least one card I can think of that exists that has done it, which is enough to show it is possible within the rules.
Otherwise, it would typically use counters, as such:
"When Degenerate Lord, Reticule enters the battlefield, put a +1/+0 counter on each Mold creature.
Put three -0/-1 counters on Reticule: Create a Meatkin artifact token."
Things to note:
- An "enter the battlefield" (ETB) effect only triggers once: literally when the creature enters play. Any creatures that would be affected by this that came in after this card was played would not gain its benefits because it was not in play when the triggered ability resolved.
- The way it is written, any Mold-subtype creatures your opponents control would get the ETB pump effect, as well.