When going alone into the queue I basically have to be prepared for all prominent threats in the game as I do not know what my teammate is using in his deck. Therefore, I need to have answers to:

- Ranged damage dealer & Siege
- Mobs
- Mass Saplings
- Turret decks & Building
- Flying units & invisable Aimbot
- Frostgoyle Factory
- Heavy damage tanks like oracle/mulch digger
- Legends

For easier comparison I use an adapted version of the 2vs2 build from the "deckbuilding with a teammate" section and will talk you through the threats and my answers to them point by point.

A basic threat in the game are ranged damage dealer. There are lots of different ways to attack or incapcitate them but you should have some to do so. A basic strategy is to summon melee units (in the deck: monks) for a direct attack on them to take them out. Spells like petrify can also incapacitate them for while. Most of the time it is advisable to address ranged damage dealer first before taking care of melee enemies because they cause more damage.

A special form of (mostly) ranged damage dealer are units with siege. Siege units deal 400% damage to fortified buildings and are therefore an immense threat to your tower and nexus. Examples are stone weavers and ballistas. For example, if the opponent attacks your tower with ballistas behind a line of tanks, you definetely want to kill the ballistas first because they a) do siege damage against your buildings and b) heal units before them.

Big mobs are best defended at the own tower with its support fire, summoned and spawned ranged own damage dealers and area of effect (aoe) damage, as well as supportive spells. This task is covered by the avenger spawner (they are dealing ranged damage on multiple targets, so somewhat aoe), marksmen spawner and my t1 summon of weavers. In the endgame I also have earthquake and the asteroidal damage of the guardian in his landing zone but also his dealing of splash damage (aoe). I can support my defense by using the spell petrify to incapacitate the opponent's units for a while.

Sooner or later you will encounter an oppenent using countless saplings to bring your towers and nexus down. While they are cute on their own, they can become a real threat in masses. Saplings quickly drain tower shots and they keep one's own units busy while the opponent's units deal damage. Especially for players that use big and slow spawners, saplings have a potential for overwhelming within the first minutes of the match. To be prepared for this, a deck should always inlcude some way of area of effect-damage (same as for dealing with mobs) and fast attacking and/or units that can target multiple units. It is advised to bring a t1 ranged damage dealer to the table. Stone weaver, the avenger spawner but also the rootdoods ability will help in sapling control in the example deck above.

Buildings can be really hard to take down without siege. Siege is multiplying the dealt damage to buildings of a unit by 4. Since damage dealing or buildings with special abilities are better brought down quickly, it is advisable to have some siege units in your deck. Weavers and the earthquake are dealing siege damage. With petrify I also got one of the few spells that can stop towers from firing.

Flying units can become a problem when you only rely on melee units. You need ranged units to attack them. T1 Weaver, Marksmen and Avenger spawner can do so.
A special case of flying units is the aimbot, which is invisable as long as no own flying unit discovers it or it is targeted by a spell. Since "energy rift" is a damage spell that can be used on the aimbot, without having sth flying of your own or a spell, you may face an invisable shooter. I am rather prepared and have flying units in my deck (avengers and spores, though one is enough).

The frostgoyle factory is a combination of the frostgoyle fountain and ammo factories producing endless of the flying and immense damage dealing frostgoyles. Better be prepared! My answer here is the spore, as I can summon it do die where I need a spore field. The spore field grounds flying units, so all of the frostgoyles get trapped and my ranged damage dealer can take care of them.

Heavy damage tanks (especially with splash damage) are better kept on a distance to your lane towers and away from your own vulnerable damage dealer. Lots of different spells and units from the different colours can be used for that. One of the green options is rooting, so that opponent units can't move. The rootdood I use as a spawner can root up to four units, when his ability is loaded with energy. This can be repeated by healing it, since this gives the rootdood energy.

Against most legends lots of ranged damage helps. :) For fighting the Guardian and Aegis siege units (weavers here again) are advised because these two legends have fortified armor.
You will have a hard time without fast attacking units against Tyrus. His shield does not waver from high damage but from multiple and fast paced attacks, the combination of weavers and Avengers is taking care of that here. Sapling charge needs similar unit style and aoe, in addition to weavers and Avengers the earthquake is of help. Against an enemy earthquake my own spawner are solid enough to withstand (Rootdood) or flying (Avengers) so therefore not affected too much. The vulnerable marksmen can be buffed with giant growth or pulse of the forest to make them more resilience. This is also of importance as marksmen can fall easily to the Soul Altar and spells like Surge of light or Hail of Arrows.