The yale is an heraldic monster characterized by two long, mobile horns, which could be swivelled independently and at will; it also has a set of fierce tusks.  The yale doesn’t seem to have a default posture; the illustrations show yales rampant.

Two forms of yale are found in period heraldry [Dennys 165].  The earlier form, the “Bedford yale”, was one of the Duke of Bedford’s supporters c.1435, and resembles an antelope.  The other form, the “Beaufort yale”, was used by his grandson Sir John Beaufort, c.1450; it is stockier, more like a goat, and is usually strewn with roundels.  However, both yales have the characteristic horns and tusks; either type may be used in Society heraldry (and specified in blazon, if the submitter insists), but no difference is granted between them.

Jacinth Aldith de Warwick bears:  Argent, a yale rampant sable, armed and attired Or, within a bordure compony erminois and vert.

Styrkárr Bjarnarson bears:  Or, a yale rampant guardant vert bezanty armed gules.

Tristan le Chantecler de Champaigne bears:  Barry azure and argent, two yales combatant Or.