Combat
Polymorphing purely to slam some gorilla fists into a baddie? This spell can really come in handy, especially if you’re low on hit points. Here are a few solid options for polymorphing for the sake of combat.
Giant Ape:
Perhaps my favorite option. The giant ape is a tank, coming in with 157 hit points, an Athletics check of +9, and a multiattack with its fists, which are both +9 to hit and do 3d10 + 6 bludgeoning damage. It also has a ranged attack option of a rock throw, so consult with your DM to see if there are any rocks in the area you could hurl for a ranged attack, or anything you can get creative with and use as a projectile, such as a gnome. The ranged weapon attack is also +9 to hit, and deals 7d6 + 6 bludgeoning.
T-Rex:
Don’t worry so much about whether you could, stop to think if you should. And yes, you should. T Rex is the largest beast you can possibly polymorph into. Besides hurling Jeeps over the sides of sheer cliffs, it also packs a mean punch in battle. These beasts are ideal for situations when you’re fighting more than one baddie. It makes a bite attack (4d12 + 7) piercing damage, which can potentially grapple an opponent Medium or smaller. It’s tail attack deals 3d8+7 bludgeoning damage. Disclaimer: these attacks cannot be used on the same target. So pick your situation wisely.
Giant Shark
Water battles can be fun. They are even more fun with you have a giant shark on your side. With 126 hit points and a swim speed of 50 feet, the giant shark is a great water option. Perhaps the best. It’s Blood Frenzy feature gives it advantage on melee attack rolls against any creature that doesn’t have all its hit points. Combine that with a +9 to hit, it’s likely you’ll land some blows. It’s bite does 3d10 + 6 piercing damage. Bear in mind it can only breathe underwater, and be sure to have a contingency plan in case your form drops in the water. Though if you’re magical enough to polymorph, you’re probably magical enough to get to dry land.
These are not the only options out there, but again, they are fun and bulky. Roll high!