It turns out, Unstable has an infinite engine. When you have a Half-Squirrel, Half-Pony
and cast any creature with an enter the battlefield effect, which all Hosts do, you are allowed to cast that creature and get that effect as many times as you want.
Ordinary Pony is a common and Half-Squirrel, Half- is an uncommon and the set has numerous was to tutor for each, so the ability for the combo to come up in limited is pretty high.
The point of Unstable is to lean towards the fun side of the spectrum and this combination while fun the first time would soon be very un-fun, so we decided to do something about it.
Black border Magic tries to avoid power level errata, but silver border tends to break black border rules, so what we did was errata Ordinary Pony to do all the fun stuff it normally does and just disallow the infinite combo.
Ordinary Pony’s Oracle text a écrit :
When this creature enters the battlefield, you may exile target non-Horse creature you control that wasn’t put onto the battlefield with this ability this turn, then return it to the battlefield under its owner’s control.
You can now bounce any creature with one name once a turn, but not more than once.
For Un-Constructed, you can still use the combo, you’ll just have to make use of R&D's Secret Lair
to remove the errata. We felt making it a four card combo instead a three card combo, will make it harder to do but still doable for those that just love their infinite combos.