MTGNexus

How do I get all creatures I control to lose all abilities and then gain another? I want it to effect creatures that enter the battlefield afterwards. This is what I have currently.

Annihilation Factor (Uncommon)
3RG
Enchantment
Creatures you control lose all abilities and gain "You may have this creature assign its combat damage as though it weren't blocked."

Since this is a static ability it will affect creatures no matter when they entered the battlefield. This wording is fine - it's the same as on Heliod's Punishment. Minor templating point: Objects "gain" abilities until end of turn and "have" them indefinitely. So you want this to say "have" and not "gain".

Be aware that losing all abilities will kill */* creatures. Before P/T were always set when abilities were striped away but in the last few years this hasn't been the case. Also it shuts off ETBs which may or may not be intentional.

You want to use Darksteel Mutation as a reference: "loses all other abilities".

Creatures you control have "You may have this creature assign its combat damage as though it weren't blocked." and lose all other abilities.

Functionally no different (except for Muraganda Petroglyphs) is this:

Creatures you control lose all abilities.
Each creature you control may assign its combat damage as though it weren't blocked.

You may want to consider whether you want the Archetype text of "[...] and can't have or gain abilities."