Immovable (SH)

You can stare down any force that bears down on you and remain unmoved.

• Increase your Strength or Constitution by 1, to a maximum of 20.
• You have advantage on Strength checks and saving throws against any spell or effect that would forcibly move you.
• When a hostile creature that you can see makes a melee attack against you and misses, you can use your reaction to shove it, so long as it is no more than one size larger than you. On success, you push it 5 feet away from you and knock it prone.

*Smiley's Homebrew