In Legacy casual, Tibalt IS somewhat playable, and that is why there is a Duel Deck dedicated to him. There are enough cards with a cheap Flashback cost that can be played from the graveyard, and cards like Browbeat. I have the duel deck on MTGO but next to no one plays Legacy on MTGO and it is proving quite the challenge to give it a spin. That will have to wait, especially now that we are in a Modern frenzy thanks to Modern Masters 2015 (and I am very much in that frenzy).
In Modern, it is quite the challenge to make him playable. To begin with, there just aren't enough cards with a cheap enough Flashback cost in Modern in Red or Red and a second color. There are enough cards to support a seemingly reasonable deck that beats face in Red and Black, mimicking the Legacy version marketed by Wizards as a Duel Deck, but that deck just didn't fly. I started by adding white in the mix, and quickly gave up that "Mardu" or WBR build. I then reverted to Red/Black.
Bloodsoaked Champion didn't cut it in this deck, but Bloodthirst worked once in a while.
Here I ultimate Tibalt, but it only happened because my opponent did not seem to get it that I could ultimate Tibalt... I played many other games in which my opponent realized Tibalt had to go and they took care that he went!
gg for this one since I took over all of my opponent's creatures.
There were many blowouts against my deck, and here is one of them. Tibalt in Red/Black in Modern.... ouch, ouch.
Here is yet another outright loss by yours truly. I turned the deck into a Grixis build to have some card draw, but it wasn't enough.
... and here is another loss
... and another