What sort of cursed future produced this overpowered Delibird and what can we do to avoid it?
All jokes aside, Iron Bundle is a potent force to be reckoned with. Base 136 Speed is patently absurd, tying with Barraskewda with only the Ice Weak Dragapult and Subpar Electrode being faster. And on such a fast Pokémon, they gave it the Ice type. What is normally one of the worst types in the game, people for years have been stating that Ice types want to be fast offensive sweepers and boy howdy does Iron Bundle fit that bill. Base 124 Special Attack is respectable, and can be pushed further with Choice Specs into absurd territory.
Really the only let down is Iron Bundle's movepool. Offensive options are limited to Ice STAB, Hydro Pump and Tera Blast. And yet as Divine Retribution has noted, that suffices. Freeze Dry is a house of a move with its type breaker vs Water types. And thanks to that, Water STAB and Ice STAB have no effective common resists. And due to how the type chart lines up, everything that resists Water gets eaten alive by Freeze Dry. And that includes Storm Drain and Water Absorb as well as the only Water Immune Pokémon that does not get shellacked by Freeze Dry is the unreleased Volcanion and Jynx (Dry Skin we have Toxicroak who does not have the bulk to tank attacks and Thick Fat we do have Walrein and Dewgong who are otherwise Subpar Pokémon). Opposing Steel and Ice types also at least resist Freeze Dry and Ice Beam, but that is small comfort when eating a Specs Hydro Pump.
And to complete this perfect storm of Stats, Iron Bundle was given 114 Defense. While this may not seem like much given its paltry HP stat, it is rather high, enabling Iron Bundle to eat powerful priority attacks that are normally the bane of speedy Pokémon as Vacuum Wave is still relegated to Lucario and Toxicroak, neither of which are especially popular right now. And it can go Tera Water or Tera Ghost to remove all of its pesky Ice weaknesses including to Mach Punch and Accelrock. And Tera Water is especially terrifying, giving Iron Bundle an accurate "Adaptability" boosted Water STAB in Tera Blast. No wonder Iron Bundle was near unanimously banned in Smogon.
Choice Scarf -counters the other most common counterplay to fast Pokémon, other Choice Scarf users
Taunt -A fast taunt is invaluable in shutting down Tanks, setup sweepers, etc.