That's an incredible and, quite frankly, unprecedented effect at instant-speed
Charizard V (Secret Rare, Champion's Path) deserves mention as the full-art partner to the VMAX that appears on the main list
You get an extra card in exile to play each turn, while opponents lose their first draw and must play from exile instead
The next turn again ensures you have 3 cards in your hand
If Sigilyph takes damage from such a foe, it will automatically be returned in full force, which will make all opposing trainers need to adjust their offense if they intend on using their strongest pokemon
But, of course, provided you're keeping two or more cards in your hand when on the receiving end of a discard spell, you should always take into account what kind of synergy or play style will emerge from keeping each set of cards