Destruction Burst
Destruction Burst is by far the best option available, bar none. It compresses both fire and darkness, and it seeks between the two, but not only that, it deals 50% more base damage than a regular spell of the same level at the cost of a negligible amount of HP.
Location: Dragonspine -> 23: Diamonds and Explosions
Cysero's Explosive Teleport Booth (PREMIUM)
This is the best option; it seeks between water and energy, and it has the same mechanics as Destruction Burst, dealing 50% more damage at the cost of a tiny amount of HP. Unlike Destruction Burst however, it requires you to buy a Z-Token package.
Location: 12000 Z-Token package
Whirl Tide
If you can't buy the 12000 Z-Token package then this is the best alternative to Cysero's Explosive Teleport Booth. It has a +6 BTH lean and a +4 BTH MC, and consists of 9 equally powerful hits. However, it deals no more damage than a regular spell.
Varrinsqu Keep -> Lavai, Shadow Storm, FallowSea
Arctic Tornado (PREMIUM)
Arctic Tornado works the same way as Cysero's Explosive Teleport Booth, and requires you to buy the 12000 Z-Token package. It compresses wind and ice, and seeks between the two.
Location: 12000 Z-Token package
Biggest Fan
This is a good F2P non-rare option for those who don't have Arctic Tornado. It's a 3-hit wind spell with a +8 BTH lean, and if all 3 hits connect, the spell can make the monster Afraid, giving them a chance of not acting for the turn.
Location: Guardian Tower -> Nimrod -> Quests (open to all) -> Arena of Enthusiasts (hard mode, no heals)
Invoke Tyrannochicken Rex (SEASONAL)
This is another nice option that returns every year during Grenwog. In terms of raw damage it is stronger than Biggest Fan, but this is due to its -10 BTH lean. In addition, unlike Biggest Fan, Invoke Tyrannochicken Rex has no MC bonus.
Location: Grenwog
No Lemons, No Melon (RARE)
No Lemons, No Melon was available from the Frostval 2015 Golden Giftboxes; thus, it's permanently rare now. It's a very nice utility option for those who like effect spells; it has a -20% damage penalty, but if one of its 3 hits connect, it will attempt to Control the monster.
Location: None
Arctic Tornado (PREMIUM)
Already mentioned in the wind section.
Location: 12000 Z-Token package
Frigid Fury
Frigid Fury is the best option for those who don't already have Arctic Tornado. The spell consists of 5 equally powerful hits, and has a +6 BTH lean as well as a +4 BTH MC bonus (so +10 BTH in total).
Location: Varrinsqu Keep -> Elder Saggidus, Cayla's Mirror, Lavai
Creation Burst (PREMIUM)
This spell works the same way as the other Burst spells mentioned here; it deals 50% more base damage than a regular spell, at the cost of a very small amount of HP. It compresses earth and light, and seeks between the two. Like Arctic Tornado and Creation Burst, it requires you to buy the 12000 Z-Token package.
Location: 12000 Z-Token package
Gravity Crush
If you don't have Creation Burst, then you should use Gravity Crush. It consists of 3 hits, with the first 2 doing 25% damage each, and the 3rd hit doing 50% damage. It has a +6 BTH lean and a +4.25 BTH MC bonus, so it gains 10.25 BTH overall.
Location: Varrinsqu Keep -> Shadow Storm, Cayla's Mirror, Lavai
Cysero's Explosive Teleport Booth (PREMIUM)
Already mentioned in the water section.
Location: 12000 Z-Token package
Pixel Storm (RARE)
Pixel Storm was part of the 2014 Frostval Giftboxes, and is permanently rare now. If you have it however, then it's the best option available to you below Cysero's Explosive Teleport Booth. It has an 8% chance of dealing 162% damage.
Location: None
MegaHyperGigaShock
This is the best energy spell available to those who don't have either of the options listed above. It consists of 6 equally powerful hits, and has 10 more BTH than a standard spell due to its lean and MC.
Location: Guardian Tower -> Guardian Shop
Truphma Surge
This is another good option, and while it deals greater damage than MegaHyperGigaShock, it has a -10 BTH lean so it's widely considered to be inferior.
Location: Robina's Shop -> Truphma Saga -> Xov's Fire -> Part 3
Thunder Wave
Thunder Wave is a great utility option; it's an effect spell with a very high chance of paralyzing the monster if the hits connect, but it has a -25% damage penalty to compensate. NOTE: If you already have Monkakazi BOOM, then use it instead as it's essentially just a superior version.
Location: Varrinsqu Keep -> Fallarion, Conflagration, Kad-Morag
Creation Burst (PREMIUM)
Already mentioned in the earth section.
Location: 12000 Z-Token package
Star Forge
If you don't already have Creation Burst, then your best option is to use Star Forge. It consists of 4 equally powerful hits, and it has a +6 BTH lean as well as a +4 BTH MC bonus.
Location: Varrinsqu Keep -> Kad-Morag, Elder Saggidus
Destruction Burst
Already mentioned in the fire section.
Location: Dragonspine -> 23: Diamonds and Explosions
ArchMage Research
Archmage Research is great. When cast, you have 3 options: Summon Mana Spirit, Dissipate Mana and Shape Mana. The Mana Spirit is a good, but situational guest that deals greater damage than normal due to shifting elements randomly. Dissipate Mana is a strong, 1-hit spell that deals Harm damage and damages the monster's MP. Shape Mana works the same way, but it damages the monster's HP instead.
Location: Devourer Saga -> Part 8 -> The Restoration