Thomas, Dungeon Assembler

When Thomas, Dungeon Assembler enters the battlefield, choose a D&D character sheet you control. Its power and toughness are equal
to two of its ability modifiers.
{w}{r}{g}: Roll a d20. If the result was equal to one of your character's ability scores, assemble a contraption. Then, if you rolled a natural 20, assemble an additional contraption and repeat this process.