Since Glenn only has one power and skulk, it can only be blocked by creatures with one or less power, which often allows you to cards when you connect to an opponent
That could be an Elesh Norn, Grand Cenobite or Avacyn, Angel of Hope you're popping into play for the low price of 3 mana and bouncing a tapped creature back to your hand, which is possibly additional upside with the right ETB creatures
You can enchant your opponents massive creature, and suddenly you can totally stonewall it with a 1/1 token or 0/1 Argothian Enchantress
Whiplash Trap and Lethargy Trap accomplish some of the same things youre looking for from the Claws and Droplets, while also being better mid-game topdecks
I can't find the guidelines for card alters that Wizards puts out (if there are any)
The mere presence of a counter means that a card can provide a benefit or be the target of spells due to its flair, in the parlance of Office Space