The Thing Under Your Bed

Fear, Hexproof, Double Strike, Trample, Indestructible, and Haste
{t}: Create 5 4/4 nightmares with fear and
hexproof
{x}{t}: Deal x damage to target creature or player
Monstrous {10}{b}{b}: If this creature isn't
monstrous it becomes monstrous
If The Thing Under Your Bed becomes monstrous, it gets 12 +1/+1 counters unless your opponent pays {12}, then The Thing Under Your Bed stops being monstrous.