Only to search for level 4 LIGHT Thunder-type monsters.
Must be normal summoned to activate its effect.
Tips, related cards, skills
Other Hunder cards
The Hunder card's specialty is their ability to swarm, allowing you to normal summon more than 1 monster per turn. The strength in numbers can lead to different playstyles. You can use cards like Enemy Controller to take control of your opponent's monster, Two-Pronged Attack / Mystic Box to destroy a difficult monster, or even The Atmosphere to take them instead. Since it's considered normal summon, you can do multiple summons even when you go against the Vagabond with the "no special summon" condition.
While Hunder cards don't really have high attack, this is good for destroying multiple low defense monsters. You can also use attack increasing cards first if you want to destroy higher defense monsters.
Pahunder and Mahunder allow additional normal summon of a level 4 light thunder monster, which Vylon Prism is. That allows for a rank 4 overlay, or level 8 synchro (because it is a tuner). It is also searchable by thunder sea horse. What is there not to get?
Well the problem isnt its rarity but rather it's released too soon.
I don't find it useless but I believe Rai-jin is definitely a good support card to increase his attack by filling up your graveyard with light monsters. If you can keep him on the field, then I see the 'hundets' becoming mid or high attack monsters.
Also to add, he gets a 200+ boost, maybe not him but the others, combine with Mako Mystic Depths Skill, Equip cards, and along with Rai-jin effect (optional) can be useful. As long as they add more thunder monsters.