What are the best strategies to playing Touchdown Mode in Clash Royale?

The same strategies you use for the normal game are relatively effective in this mode as well with a few tweaks. Units that have speed increases are good, especially the battle ram since it only targets buildings. Like Kyle said in the comments, this lets you do a sneaky strategy where you put some kind of tanky unit on one side like a PEKKA or a lava hound and then put a faster unit on the other side when they've played their hand.

A building unit is a must have in order to stop strategies like this and if I remember correctly, there are areas where bigger buildings can draw aggro from both sides. You also should have some flying units like bats or minion horde to DPS down melee units and tanks but do not rely heavily on them (keep a dedicated tank killer in your team). Spawners like witches and night witches along with exploders like lava hound and skeleton barrel occasionally cheese a round win off of not being stopped in time or left alone for too long. To counter these, make sure you have some AoE in your squad with a bowler for ground troops/tank and/or a baby dragon for the air.

A lot of the units I mentioned are pretty high cost so you need to balance around what you find the most important. Each high elixir unit has a lower cost replacement and some can play two roles (bowler = tank + ground AoE). Your spells should also be relatively low cost and mostly used for dealing with low cost units (think zap, arrows, log, barbarian barrel) unless you are going for a cheese win with a battle ram + rocket on whatever building they put up.

A good check list for making a starting deck is something like this:

• Tank 5-7 elixir
• AoE clear (arrows, zap) 2-3 elixir
• Push back spell (tornado, log, barbarian barrel) 2-3 elixir
• Tank killer most are 4 elixir
• Ranged DPS like musketeer or electro wizard if you have it 3-4 elixir
• Fast flying group unit 2-5 elixir
• Building any will do so just take the one that best completes your deck
• Fast/exploder unit that ignores troops battle ram/skeleton barrel 3-4 elixir

This is just a general layout of a good all around deck for this game mode. With this kind of setup, you do not have to worry as much about what your teammate has. All strategies are much easier if you have a duo partner so you can make decks that compliment each other but that is a whole different question in my opinion. Obviously, some of these unit types can overlap so you have room to take a few buildings, tanks, ranged units, etc depending on what you feel you need. Cater your deck to what you have that is strong and just try to have some fun with it.

Hopefully this helps you out a bit as there is not a "correct answer" so to speak for a question about best decks.