NR: Love the flavour! I think a catapult ought to kill the creatures it gives flying at the end of the turn (or at least, do some damage to them. Lean into the flavour!)

2 mana noncreature source which can ping each turn is deceptively strong and oppressive to the point of format warping (ala how for example bowmasters has been pushing out classics such as bob from legacy top tier status).

Is a 4 mana uncommon a bit less overpowered?

­Rod of Ruin was to cast and to activate, but then again it was never really that great.

It should be noted though that not having a mana cost at all associated with the activation is a meaningful boost to the strength of this kind of effect.