There are many different Pokemon with just as many type combinations to take advantage of.
While a lot of Pokemon have one pure type, trainers wouldn't have much difficulty stepping into the tall grass and finding a creature with two types to its name.
Type combinations are essential in Pokemon. They add or remove potential weaknesses. They boost the same type attacks available to use. Overall, having more than one type can be very beneficial.
Note: This article is subjective and reflects the opinion of the writer.
Top 5 Pokemon type combinations
#5 - Dark/Psychic
Malamar is a great example of a Dark/Psychic-type Pokemon. The typing is great at remaining unscathed. It doesn't have any resistance, but it is granted immunity to Psychic-type moves.
It only has two weaknesses: Fairy and a 4x weakness to the rarely used Bug. Every other type just does normal damage against Dark/Psychic.
#4 - Steel/Flying
Steel/Flying is a wonderful type combination. Corviknight has proven this to be true. It is immune to Poison and Ground. It is only weak to Electric and Fire. It also resists a whopping seven different types.
Steel/Flying Pokemon are few and far between but definitely have one of the better type combos. It would be even higher on the list if its weaknesses weren't so common.
#3 - Fire/Steel
The prime example of a Fire/Steel-type Pokemon is the Legendary Heatran. A double weakness to Ground can be devastating, but it makes up for it elsewhere.
It is immune to Poison and has a massive nine resistances. Five of those resistances are doubled due to the type combination. That is some solid defense.
#2 - Fairy/Steel
Steel just keeps on winning. Matched up with Fairy, like in the case of Zacian, it becomes even more of a defensive juggernaut. This combination comes with nine resistances and two weaknesses to Fire and Ground. It also allows for immunity to the incredibly powerful Dragon and Poison-types. It is almost unfair.
#1 - Water/Ground
Water/Ground is incredible, as shown by Swampert and Gastrodon. The only issue is its glaring weakness to Grass-type attacks. It is immune to Water's natural enemy, Electric. It resists Poison, Rock, Steel, and Fire.
Everything else is just normal damage. If STAB attacks are taken into account, everything it resists or is immune to are in for big trouble.