Beartic in his current state appears as such:
Type: Ice
Stats: 95 HP/ 110 Attack/ 80 Defence/ 70 Special Attack/ 80 Special Defence/ 50 Speed
Possible Abilities include: Snow Cloak and Swift Swim
Mega-Beartic could have:
Type: Ice/Fighting
Stats: 95 HP/ 140 Attack/ 120 Defence/ 60 Special Attack/ 120 Special Defence/ 50 Speed
Ability: Refrigerate
Possible Design: http://pokecharms.com/data/attachment-files/2015/02/170609_Beartic_-_Mega_Evolution.png
This type would allow him to take advantage of stab Superpower which is already in his move list. I decided to drop 10 points off of his special attack because it was never utilised, and because doing so would allow me to get more out of the mega evolution. With this stat distribution, I decide to leave his speed alone; firstly, so that he could still operate under trick room effectively and secondarily it is too low to be improved upon without having to invest more points than I am comfortable with. The boosts to attack, defence, and special defence are to further improve the abilities of Beartic. The ability is to couple with the Pokedex reports of Beartic saying he can freeze paths across the water in order to cross it, and to give him a harder hitting stab move with Return/Double-Edge/Slash.
In a competitive sense, Mega Beartic could be placed in OU or BL tiers as he is able to handily defeat many of the threats in the tier such as Landorus-Therian, Excadrill, and Garchomp. However, he is not so powerful as he would dominate the tier he is dispatched by Lucario, Mega Charizard X, Blaziken, Talonflame, and Mega Altaria.
This mega would bring new viability to a Pokemon that has been fairly forgotten in the competitive scene and I feel it could bring new life into a Pokemon that is just so close to being great.