Red Dragon Lair, like Ancient Den consists of only one boss to fight through, Veraaksia and when using the right strategy is quite easy to beat. This boss in both normal and hard levels only uses unique dragon cards, mainly dragon whelps which have an effect similar to the skeleton's reaping curse and dragonkin which have an effect similar to the Crowned Nid's Stampede, all the while summoning magma pools, portals and casting spells.
Boss: Veraaksia, 100/200 Hp
Unique Cards: Flame striker, Flame Whelp and Flame Dragonkin(yep only unique cards)
Recommended Cards: Pegasus
Both normal and hard are essentially the same with the only significant difference apart from the obvious power jump in cards being Veraaksia in hard uses a unique 1x2 AoE ability, dragon claw that instantly kills any unit. There are two main approaches to this boss fight. The first involves forcing down the boss with rushing units. Units with mobility and damage growing potential such as Knight , Champion Knight and Fenris the Butcher can quickly take care of the boss given enough time. In particular Black Rider and Doom Rider can negate the damage of the dragon whelps that the boss throws out while quickly growing in damage.
In turns 6, 13 and 18 the boss casts a massed version of Forgetfulness and Armageddon so it's best to place these types of units directly after those turns to get the most out of the units. This only occurs when 2-3 player units are on the field.
The boss summons portals in response to units placed. A popular strategy is to wait until turn 6 before placing any units to avoid summoning too many whelps.
The priests Blessing: Sanctuary spell will save units from Armageddon's as it isn't effected by forgetfulness. It won't however save units from magma or the hard bosses dragon claw. Dispel can be used on units with innate ability to allow them to continue gaining damage.
The second and easiest approach involves reflecting Veraaskia's special skill which deals 99 damage down the first column next to the players. This requires casting Blessing: Sanctuary on a column of walls. At least two Sanctuary's are needed, placing them on walls in row's 1 and 3 which reflects 198 damage however a third is usually used, placed on the wall in row 4.
The skill is only used onward from round 12. Attempting it beforehand is a waste.
Weaker walls have the advantage of being ready whenever they are needed, however they are extremely susceptible to magma tiles as Sanctuary cannot prevent magma damage. This can be mitigated through Blessing: Resistance, Petrify or higher tier walls.