Cake Golem

Made of cake.  It's a small golem, but instead of clay, it's made of cake.

Keep it cool. Whenever the golem is subjected to cold damage, it takes no damage and instead regains a number of hit points equal to the cold damage dealt.

More Icing!  The golem is immune to any spell or effect that would alter its form. however, each time a cold spell used on it hits, it gains 1d12 + 10 temporary hitpoint, and every 30 temporary hitpoints make it grow in size (maximum size: Huge) as more and more sugary icing is added to its form, transforming the frost from the attack on beautiful and delicious icing decoration.

Too Hot!  The golem has vulnerability against fire type of damage. Its size diminishes (minimum size: Small) when its total hitpoint is lower than 40.

My candles!  Whenever the golem starts its turn with 60 hit points or fewer or the candles on its back are extinguished, roll a d6. On a 6, the golem goes into the "angry" stage. On each of its turns while "angry", the golem attacks the nearest creature it can see. If no creature is near enough to move to and attack, the golem attacks an object, with preference for an object smaller than itself. Once the golem goes berserk, it continues to do so until it is destroyed or regains all its hit points or its candles are re-ignited.

Magic Resistance. The golem has advantage on saving throws against spells and other magical effects.

Magic Weapons. The golem’s weapon attacks are magical.

I'm not just a cake! (Multiattacks). The golem makes two slam attacks.

Icy Punch!(Slam). Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 16 (2d10 + 5) bludgeoning damage. If the target is a creature, it must succeed on a DC 15 Constitution saving throw or be englued (speed reduced to 0 and can't use any dash action) into a pillar of made of icing and must retry the saving throw at each end of its turn. For Each turn spent inside of the pillar, the creature takes (1d12+5) cold damage. 

It's slippery! (Recharge 1d4)  Range Weapon Attack: Use 1d12 of its hit points to throw some icing on the ground, up to 30 ft range. Every creature walking in the iced area must succeed on a DC 14 Dexterity saving throw or be knocked prone on the ground. 

Here I come! (Recharge 1d6). Until the end of its next turn, the golem magically gains a +2 bonus to its AC, has advantage on Dexterity saving throws, and can use its slam attack as a bonus action.