potential design for both self bounce and GW

That can get fairly complex pretty fast IMO. Say, if you have two of these on the board, then drop couple of creatures (with token generation for example), and distribute the buffs evenly... I mean, I could see that being a pain to manage and keep track of. Add in the possibility of flash creatures and it's a real mess IMO. I would suggest redflagging this (ie. keeping an eye out for it).

Taking a quick glance at the cards in the set, I also see (((Banner Runner))) at common that could pronounce this potential issue of temporal buffs.

Seconded - at common I would expect this either to only trigger on itself ETBing or only pumping e. g. itself.

Or maybe have it always pump the creature that ETBs. Though that kinda has the downside of improving creatures that are summoning sick.

Yeh I need a ETB effect for a green common but this is an overreach the more I think about it