Two will make you happy. The third feels like a cheat.
Continuous Trap Card
Activate by targeting 1 Dragon-Type monster you control with 2500 or less ATK and DEF.
(1) Neither player can Special Summon monsters whose ATK is lower than or equal to the target’s original ATK.
(2) When that monster leaves the field, destroy this card.
Normal Trap Card
(1) When an opponent’s monster attacks you directly: End the Battle Phase, then, you can Special Summon 1 Tuner and 1 Synchro Monster from your Graveyard, but their effects are negated.
Mathematician in “Descend of the True Emperor”
Source: The Official YGO Twitter