Enchantment
Creatures with flying can't attack you or planeswalkers you control.
At the beginning of your end step, create a 5/5 green Wurm creature token.
Once a creature has attacked you or a planeswalker you control, it will remain in combat even if it gains flying. Similarly, if a creature with flying enters the battlefield attacking, Sandwurm Convergence's first ability can't undo that attack.