This also is a power-flip from jade Druid to Jade Rogue. Jade Druid losing Brann is a blow, but this plus Jade Swarmer seems nice. Plus if you can conceal this in wild, you can combo with shadowstep to do some craziness (steal two minions with sylvanas and still have it on the board!)
"Insane"? 8 mana, summon a 3/4, a 4/3 and a random 2 drop? I mean, Silver Hand Knight is a 5 mana, summon a 4/4 and a 2/2, so you could play a better turn with SHK + Spider Tank (or Bronn + SHK for more value).
People are over-hyping this. It's not as strong as Brann.
Yes, think if you get a 2 drop with deathrattle like Pyros or mad scientist, you get a 3/4, a 4/3, a 2/2 and a free secret or a free draw, even a creep or a gnome is awesome too.
Yes, that's good value. But don't forget what turn you are playing this on. It's turn 8. You need to be doing more than eking out an extra card draw without even touching the opponent's board. The opponent's an elemental shaman and he has a 6/6 Blazecaller on the board, and you're going to play 3 minions with 4 health or less? Kalimos, Primal Lord says Hi and you're dead. You're facing a Jade Druid? LOL, you play three small minions, he'll play three big ones. You're facing a Mage? Flamestrike. Facing a Priest? Dragonfire Potion. Warlock? Felfire Potion.
No one will play Umbra on turn 4 unless they're against aggro and need anything on the board. You play it late game. But what do you combo it with? The best combos for value require 8+ mana and net you an extra 4/5 at best, and does nothing to the opponent's board. That's value, but at that point of the game you're less concerned with squeezing value out of your cards and either setting up your win condition or stopping the opponent's. Brann at least let you combo with battlecries that affected the board like Blackwing Corrupter, or insane ones like Kazakus.
It's a good card, it'll be played, but people thinking it's the same power as Bronn are mistaken. The most likely combo's will be the small ones, like with Crystalline Oracle or one of the small Rogue deathrattles. The late game big-value combo's are just too slow and not impactful enough unless you are in Wild and pull off a Sylvannas combo.